Preparation method and application of large-size tungsten-doped ni-fe nanowire electrocatalyst

Abstract

The application provides a preparation method of a large-size tungsten-doped NiFe nanowire electrocatalyst, wherein the foam nickel is immersed in a corrosion solution containing Fe and W for 3-15 minutes to obtain a W-doped NiFe catalyst. The nanometer structure of the catalyst is an ordered nanowire with a diameter of 40-60 nm, and there is no agglomeration phenomenon, which is beneficial to the exposure of active sites and the release of oxygen, and the dense structure can improve the stability of the catalyst. When the W-NiFe catalyst is applied to an oxygen evolution reaction, the overpotential is only 143.7 mV when the current density is 10 mA cm ‑2 , and the catalyst can be stably operated for 150 hours under a current density of 500 mA cm ‑2 . The catalytic performance and stability of the catalyst are superior to those of a noble metal IrO2.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to the large-scale preparation of tungsten-doped NiFe (W-NiFe) nanoparticle electrocatalysts and their application in oxygen evolution reaction. Background Technology

[0002] Currently, most methods for preparing NiFe-based oxygen catalysts require complex processes, such as hydrothermal methods, electrodeposition, and chemical vapor deposition, and the reaction process needs to be carried out at high temperatures of 100-300℃. In addition, subsequent high-temperature calcination is required to achieve phase transformation (alloying, carburization, etc.), which places extremely high demands on the preparation conditions and equipment, undoubtedly increasing manufacturing costs.

[0003] Most NiFe catalysts exist as powder samples with extremely low yields, requiring the addition of binders and conductive agents to prepare self-supporting electrodes, making large-scale industrial application difficult. For example, in the patent "A Preparation Method and Application of a Tungsten-Doped Electrolytic Water Catalyst," the preparation process requires a hydrothermal reaction at 120–170°C for 4–8 hours, followed by a further hydrothermal reaction at 150–170°C for 6–10 hours during sulfidation. This time-consuming, energy-intensive, and cumbersome preparation method makes it difficult to achieve large-scale, large-size catalyst preparation. Furthermore, the preparation of large-size electrodes makes it difficult to control the micro-nanostructure, hindering the fabrication of ordered nanowire arrays. The consistency, uniformity, repeatability, and nanostructure control of large-size self-supporting electrodes have not been studied. Regarding catalyst applications, the prepared catalysts can only be used at low current densities (10–50 mA cm⁻¹). -2 It cannot operate under industrial operating conditions (~400 mA cm⁻¹). -2 It achieves long-term stability (at 50℃). Summary of the Invention

[0004] To address the issues of complex, costly, time-consuming, and equipment-intensive processes in the preparation of NiFe electrocatalysts, a one-step method is proposed. The large-scale, large-size preparation of NiFe catalysts was achieved.

[0005] This invention enables the uniform, homogeneous, and reproducible preparation of large-size electrocatalysts, as well as the ordered synthesis of NiFe nanowire catalysts, thereby achieving microstructure control of the catalysts.

[0006] The technical solution of this invention improves the stability and catalytic activity of the catalyst in the hydrogen production and oxygen evolution reaction of water electrolysis under industrial operating conditions.

[0007] This invention provides a tungsten-doped NiFe (W-NiFe) nanoparticle electrocatalyst. Nickel foam is immersed in a corrosion solution containing Fe and W ions for 3-15 minutes at an immersion temperature of 25-65°C to obtain a W-doped NiFe catalyst. The prepared catalyst exhibits a nanowire array structure.

[0008] The nickel foam was obtained by sequentially sonicating it in ethanol, hydrochloric acid, and deionized water, followed by drying it with lint-free paper.

[0009] The tungsten source in the corrosion solution is selected from any one of sodium tungstate, tungsten oxide, tungsten sulfide, and tungsten carbide, and the concentration of the tungsten source is 0.05-10 mmol / L.

[0010] The iron source in the corrosive solution is selected from any one of ferric chloride, ferric nitrate, and ferric sulfate, and the concentration of the iron source is 1-50 mmol / ml.

[0011] The preparation process is characterized by its simplicity and speed, eliminating the need for complex processes (such as electrodeposition, high-temperature calcination, and expensive advanced preparation techniques). It enables large-scale, large-size preparation of catalysts (the large size described in this invention refers to a size specification of at least (10-20 cm) × (10-20 cm)). Furthermore, it allows for in-situ doping of tungsten at low temperatures. The large-size NiFe catalyst exhibits consistency in nanostructure and catalytic performance, possessing an ordered nanowire array structure and demonstrating excellent catalytic performance in the oxygen evolution reaction.

[0012] This invention enables the large-scale preparation of tungsten (W)-doped NiFe catalysts via a one-step method (the preparation container can be expanded, and the preparation size can be further increased). Moreover, the catalysts have excellent consistency in composition and structural properties, enabling large-scale preparation of catalysts on an industrial scale.

[0013] The catalyst's nanostructure consists of ordered nanowires with a diameter of 40-60 nm, exhibiting no aggregation, which facilitates the exposure of active sites and oxygen evolution. The dense structure also enhances the catalyst's stability.

[0014] W-NiFe catalyst was applied to the oxygen evolution reaction at a current density of 10 mA cm⁻¹. -2 The overpotential is only 143.7 mV, and it can withstand current densities up to 500 mA cm⁻¹. -2 It can operate stably for 150 hours and is superior to the precious metal IrO2 in terms of both catalytic performance and stability.

[0015] The method of this invention for preparing W-NiFe catalysts is simple and easy to prepare on a large scale and industrially. The catalysts exhibit excellent catalytic performance in the oxygen evolution reaction and show great promise for practical applications in water electrolysis for hydrogen production, carbon dioxide reduction, and metal-air batteries. Attached Figure Description

[0016] Figure 1 A schematic diagram of the preparation of W-NiFe catalyst.

[0017] Figure 2 The image shows a physical sample of the W-NiFe catalyst prepared in Example 1 during large-scale production.

[0018] Figure 3 Linear sweep voltammetry (LSV) curves of five typical regions in a large-size catalyst.

[0019] Figure 4 High-resolution electron microscope image of NiFe catalyst.

[0020] Figure 5 High-resolution electron microscope image of a tungsten-doped (W-NiFe) catalyst.

[0021] Figure 6 LSV curves of W-NiFe, NiFe and IrO2.

[0022] Figure 7 W-NiFe and IrO2 at a current density of 500 mA cm⁻¹ -2 Stability testing during operation.

[0023] Figure 8 Linear sweep voltammetry (LSV) curves of catalysts prepared by adding different types of sodium salts.

[0024] Figure 9 Linear sweep voltammetry (LSV) curves of catalysts prepared with different sodium salt addition amounts.

[0025] Figure 10 Linear sweep voltammetry (LSV) curves of catalysts prepared under different temperature conditions. Detailed Implementation

[0026] Example 1 use Figure 1 The preparation process of the W-NiFe catalyst is illustrated in the schematic diagram below: Commercial nickel foam (NF 15×20 cm) 2The nickel foam was continuously sonicated in ethanol, hydrochloric acid (3 M), and deionized water for 15 minutes, and then dried with lint-free paper. Separately, 10 mmol of sodium tungstate was added to a 25 mM FeCl3·6H2O solution to form a homogeneous solution. Clean nickel foam was then placed in the homogeneous solution and reacted at 45 °C for 10 minutes. After cooling to room temperature, it was dried to obtain the large-size electrocatalyst.

[0027] Figure 2 A large 300 cm² size was prepared using a simple method. 2 The catalyst (whose size can be easily further increased if the preparation container is enlarged) exhibits good uniformity, with consistent color across all parts, indicating the consistency of its composition and structural properties. The transformation from the original nickel foam to a self-supporting electrode with a brownish-yellow surface achieves a uniform and consistent formation of the catalytic active layer.

[0028] Figure 3 Linear sweep voltammetry (LSV) curves for five typical regions in the large-size catalyst prepared in Example 1. Note: Selected... Figure 2 The LSV curves of the five typical regions in the large-size electrode show good overlap, indicating that the large-size catalyst has good consistency in catalytic activity.

[0029] Figure 5 This is a high-resolution electron microscope image of the tungsten-doped (W-NiFe) catalyst. It can be seen that the microstructure of the W-NiFe catalyst is an ordered nanowire structure (10-20 nm). The nanowires are arranged in an orderly manner to form a dense structure similar to nanowire clusters. This ordered structure facilitates electron / mass transfer during the oxygen evolution reaction, accelerates the desorption and rapid release of oxygen bubbles at high current densities, provides more reaction sites for active sites and reaction intermediates, and improves the overall activity and stability of the catalyst.

[0030] In the steps of Example 1 above, only sodium tungstate was not added, and the resulting catalyst was a NiFe catalyst. Figure 4 This is a high-resolution electron microscope image of the NiFe catalyst. The image shows that the catalyst's microstructure is disordered, with a rough and uneven surface.

[0031] This application focuses on the current density detection of the W-NiFe electrocatalyst prepared in Example 1, as well as the NiFe electrocatalyst and commercially available noble metal IrO2. The tests were conducted in a three-electrode system with the prepared self-supported catalyst as the working electrode, a Hg / HgO electrode as the reference electrode, and a carbon black electrode as the counter electrode. The electrolyte was a 1 M KOH solution. Linear sweep voltammetry (LSV) measurements showed that the overpotential of W-NiFe at the same current density was lower than that of the NiFe catalyst and the noble metal IrO2, exhibiting excellent catalytic activity. This can be attributed to the nanowire array structure facilitating electron / mass transfer, accelerating the desorption and rapid release of oxygen bubbles at high current densities, and providing a better reaction site for active sites and reaction intermediates. Furthermore, the dense nanowire structure effectively prevents the catalyst from collapsing during operation, while the strong direct coupling between the active layer and the metal substrate prevents the detachment of active material at high current densities, thereby improving the overall activity and stability of the catalyst. The results are as follows: Figure 6 , 7 As shown.

[0032] from Figure 6 As can be seen from this, the W-NiFe electrocatalyst operates at a current density of 10 mA cm⁻¹. -2 The overpotential of W-NiFe is only 143.7 mV. Furthermore, the overpotential of W-NiFe at various current densities is lower than that of noble metal IrO2 and the original NiFe catalyst, indicating its excellent catalytic activity and great application potential under practical conditions.

[0033] from Figure 7 It can be seen from this that W-NiFe at 500 mA cm⁻¹ -2 W-NiFe maintains good stability under high current density, with its overpotential increasing by only about 233 mV after 150 hours of testing, while the overpotential of noble metal IrO2 increased by 726 mV after about 120 hours of testing. This indicates that W-NiFe has excellent stability and is more suitable for oxygen evolution reaction under high current density conditions.

[0034] Example 2 The methods and steps are the same as in Example 1, except that sodium tungstate is replaced with sodium phosphate, sodium hypophosphite, sodium vanadate, sodium fluoride, sodium sulfate, or sodium molybdate. The effects of different sodium salts on the corrosion solution were analyzed, such as sodium phosphate, sodium hypophosphite, sodium vanadate, sodium fluoride, sodium sulfate, sodium molybdate, and sodium tungstate. Figure 8 As can be seen, the addition of various types of sodium salts improves the catalytic performance. Among them, the addition of sodium tungstate can greatly improve the catalytic performance and exhibit the lowest overpotential at the same current density. This result strongly confirms that tungsten doping can effectively improve the catalytic activity of the catalyst in the oxygen evolution reaction.

[0035] Example 3 The methods and steps are the same as in Example 1, only the amount of sodium tungstate was adjusted, specifically to 0, 0.05 mmol / L, 2 mmol / L, 5 mmol / L, and 10 mmol / L. The amount of sodium salt added also has a certain impact on catalytic performance, such as... Figure 9 As shown, the synthesized W-NiFe catalyst exhibited optimal performance when the amount of tungstate added was 2 mmol / L, while both low concentrations (0.05 mmol / L) and high concentrations (10 mmol / L) improved the catalytic performance. Too low a concentration of sodium salt would fail to effectively regulate the electronic structure within the catalyst, while too high a concentration would cause the doped anions to overflow from the surface. Therefore, the sodium salt addition range in this patent is 0.05 mmol / L–10 mmol / L.

[0036] Example 4 The methods and steps were the same as in Example 1, only the reaction temperature was adjusted. Specifically, the temperatures were 25℃, 45℃, 65℃, and 85℃. The effect of temperature on catalytic performance during the preparation process was explored, such as... Figure 10 As shown, the catalytic performance is optimal at 65℃. This can be attributed to the fact that the corrosion reaction rate is too slow below 65℃, the reaction area is uneven, the formed catalyst lacks density, and it is difficult to achieve uniform performance in a large-area catalyst. When the temperature is above 65℃, the corrosion reaction rate is too fast, and Fe ions easily react excessively with the metal substrate, resulting in poor mechanical properties of the self-supporting electrode and collapse of the surface structure of the catalytic active layer, thus leading to a decline in catalytic performance.

Claims

1. A method for preparing large-size tungsten-doped NiFe nanowire electrocatalyst, characterized in that, Commercial nickel foam NF 15×20 cm 2 The catalyst was subjected to continuous ultrasonic treatment in ethanol, 3 M hydrochloric acid, and deionized water for 15 minutes, and then dried with lint-free paper. In addition, 10 mmol of sodium tungstate was added to 25 mM FeCl3·6H2O solution to form a homogeneous solution. Clean nickel foam was then placed into the homogeneous solution and reacted at 45 °C for 10 minutes. After cooling to room temperature, it was dried to obtain a large-size tungsten-doped NiFe nanowire electrocatalyst. The microstructure of the tungsten-doped NiFe catalyst is an ordered nanowire structure with a nanowire size of 10-20 nm.

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