Preparation and application of electrolytic seawater catalyst for adjusting local atomic environment

Abstract

This invention relates to a method for preparing and applying a seawater electrolysis catalyst by modulating the local atomic environment through P doping and oxygen vacancies. The technical solution involves: simple cleaning of a self-supporting material, followed by the preparation of a FeOOH precursor using a molten salt method, and then obtaining a modified P-Fe3O4 electrocatalyst through phosphating calcination and reduction treatment in NaBH4 solution. This achieves efficient hydrogen production under industrial seawater conditions while maintaining long-term stability. The beneficial effects of this invention are: by modulating the local atomic environment of Fe3O4 through P doping and O vacancies, the hydrogen adsorption kinetics at Fe sites on P-Fe3O4-x are promoted, and the Cl- concentration is reduced. ‑ The adsorption energy of Fe active sites in Fe3O4 effectively inhibited Cl adsorption. ‑ This reduces toxicity while improving the long-term stability of the catalyst, solving the slow kinetics problem in alkaline seawater electrolysis and providing possibilities for subsequent industrial applications.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of engineering materials, and particularly relates to a preparation method of a P-doped O-vacancy-rich self-supporting Fe3O4 electrocatalyst and application of the electrocatalyst to large-current seawater electrolysis. BACKGROUND

[0002] Water electrolysis for hydrogen production is a key technology for green hydrogen production, and the hydrogen evolution reaction (HER) is a crucial half-reaction therein. At present, almost all reported HER studies use high-purity freshwater as raw material, ignoring the most abundant seawater resource on earth. Seawater electrolysis is a promising alternative method, especially in arid regions where freshwater is scarce. So far, Pt-based materials have been recognized as the most effective HER catalysts. However, high price and scarcity seriously limit their widespread and industrial applications. Abundant Fe3O4 on earth as a possible alternative to noble metal-based catalysts, because its octahedral iron site can promote the H2O dissociation process, providing hydrogen intermediates in alkaline media. However, there are several very big challenges to achieve high catalytic activity of Fe3O4-based HER catalysts in seawater. On the one hand, Fe3O4, although having a favorable water dissociation energy, has poor hydrogen adsorption capacity, which affects the reaction efficiency. Another key issue to consider is that there are 0.5 M Cl - in natural seawater, which can poison the catalyst and limit its long-term stability. In addition, the catalytic activity of the electrocatalyst is further reduced with the increase of salt concentration in the seawater splitting process. Therefore, it is necessary to adjust the local atomic environment of the Fe3O4-based catalyst to improve hydrogen adsorption and salt tolerance, especially at large current densities.

[0003] In these studies of Fe3O4-based HER catalysts, common effective strategies including heteroatom doping have been proven, which can improve the intrinsic catalytic activity of HER by adjusting the hydrogen adsorption energy. For example, the electronic structure of Fe atoms in Fe3O4 was adjusted by using a Ni doping strategy to achieve a suitable hydrogen adsorption energy [J. Energy Chem. 73 (2022) 330-338]. In terms of preventing the poisoning of materials by Cl - , previous studies have mostly focused on constructing a barrier to Cl -protective layer to inhibit the above-mentioned possible toxicity [J. Clean. Prod. 182 (2018) 529-537; ACS Catal. 8 (2018) 457-465; ACS Nano. 10 (2016) 11428-11433]. However, due to the fact that the modified layer is usually not stable enough under harsh operating conditions, such repulsion strategy of the modified layer is faced with the problems of durability and undesirable mass transport [Adv. Energy Mater. (2023)]. In addition, there is no report on the research of adjusting the local atomic environment of Fe3O4 in seawater by utilizing the tandem effect.

[0004] A P-doped O-vacancy self-supported Fe3O4 electrode (P-Fe3O4-x) is constructed herein as a highly efficient and stable HER catalyst under alkaline seawater. P-doping and O-vacancy adjust the local atomic environment of Fe3O4, promoting the hydrogen adsorption kinetics of Fe sites on P-Fe3O4-x. In addition, the tandem shielding effect reduces the Cl - adsorption energy of the Fe active site of Fe3O4, effectively inhibits the toxicity of Cl - , and at the same time improves the long-term stability of the catalyst. This study provides a new idea for designing efficient hydrogen production electrocatalysts for large-scale seawater electrolysis. SUMMARY

[0005] The purpose of the present application is to provide a synthesis method of a P-doped O-vacancy self-supported Fe3O4 material. First, FeOOH precursor is prepared by molten salt method. Then, the prepared FeOOH is phosphated in an inert atmosphere at 350℃ to obtain P-Fe3O4. Finally, P-Fe3O4 is immersed in NaBH4 solution of different concentrations at room temperature. Under highly reduced conditions, P-Fe3O4-x with a large number of oxygen vacancies can be generated. Compared with the traditional method of preparing HER electrocatalysts, the present application solves the problem of slow kinetics in the process of alkaline electrolysis of seawater, ensures efficient catalysis, and can maintain catalytic stability under high current density conditions, providing the possibility for subsequent industrial practical application

[0006] To achieve the above object, the technical scheme of the present application is as follows:

[0007] The present application provides a preparation method of a P-doped O-vacancy self-supported Fe3O4 electrocatalyst, which can be realized by the following technical route:

[0008] (1) Pretreatment of self-supported material: after the self-supported material (foamed iron) is cut into appropriate size, it is respectively immersed in hydrochloric acid, acetone and deionized water for ultrasonic treatment, and then dried in a vacuum oven.

[0009] (2) Preparation of FeOOH precursor: Fe(NO3)3·9H2O was heated to melt in an oven at 130-170℃, and the pretreated foamed iron was immersed in the molten salt for 5-60 min and then naturally cooled to room temperature. After repeated washing with deionized water and ethanol, it was dried in a vacuum oven.

[0010] (3) Preparation of P-Fe3O4: The FeOOH sample was annealed in N2 at 300-400℃ for 1-3 h, with a heating rate of 1-3℃ / min. During the annealing process, NaH2PO2 (0.5-2 g) and FeOOH sample were placed in the upstream and downstream of the tube furnace, respectively.

[0011] (4) Preparation of P-Fe3O 4-x : At room temperature, the obtained P-Fe3O4 was immersed in a 0.1-0.5 M NaBH4 solution for 30-90 min, and then dried in a vacuum oven after repeated washing with deionized water and ethanol.

[0012] According to the preparation method of the technical route, the foamed iron in step (1) is cut into 1 cm*2 cm in size, and is immersed in hydrochloric acid, acetone and deionized water for ultrasonic treatment for 10-40 min and then dried to remove organic matter and oxides on the surface of the foamed iron.

[0013] According to the preparation method of the technical route, the heating temperature of the oven in step (2) is 130-170℃, and the reaction time in the molten salt is 5-60 min to synthesize ellipsoidal nanoblock FeOOH precursor with uniform size and shape. According to the preparation method of the technical route, the temperature in N2 in step (3) is 300-400℃, the annealing time is 1-3 h, the heating rate is 1-3℃ / min, and the amount of NaH2PO2 is 0.5-2 g.

[0014] According to the preparation method of the technical route, the immersion time in the NaBH4 solution in step (4) is 30-90 min, and the immersion concentration is 0.1-0.5 M.

[0015] The application also provides the application of the P-doped O-vacancy self-supporting Fe3O4 material prepared by the above technical route in industrial electrolytic seawater hydrogen production.

[0016] As a further feature of the application: the P-doped O-vacancy self-supporting Fe3O4 material prepared by the above preparation method is used as a HER electrocatalyst for electrolyzing seawater in an anion exchange membrane electrolyzer, which has excellent electrochemical performance. In alkaline seawater (1 M KOH seawater), only 1.97 V working voltage is needed to achieve 1 Acm -2The current density is 10 mA / cm2, and the material can be stably operated for more than 100 hours under industrial seawater conditions.

[0017] The application provides a preparation method of a P-doped O-vacancy self-supporting Fe3O4 HER electrolytic seawater electrocatalyst. Compared with a traditional preparation method of an HER electrocatalyst, the application serially connects the double effects of P doping and O vacancy, ensures efficient catalysis, can maintain catalytic stability under a large current density, and has important value in future practical application of seawater electrocatalysis. DETAILED DESCRIPTION

[0018] The technical solutions of the application will be clearly and completely described below in combination with specific embodiments, but the application is not limited to the following examples. Any modification within the concept and scope of the application is within the protection range of the application. The test methods in the following examples are conventional methods, and the instruments and materials are commercially available unless otherwise specified.

[0019] Example 1

[0020] A synthesis method of a P-doped O-vacancy self-supporting Fe3O4 for electrolysis of seawater to produce hydrogen comprises the following steps:

[0021] (1) In this embodiment, a 1 cm*2 cm foam iron is cut, and the foam iron is placed in hydrochloric acid, acetone and deionized water for ultrasonic treatment for 30 min, and then vacuum dried for standby.

[0022] (2) Fe(NO3)3·9H2O is heated to melt in an oven at 150 DEG C, and the pretreated foam iron is immersed in the molten salt for reaction for 20 min and then naturally cooled to room temperature. After being repeatedly washed with deionized water and alcohol, the material is dried in a vacuum oven. The scanning electron microscope of the material is ellipsoidal nanoblock-shaped as shown in the figure. Figure 1 )。

[0023] (3) The FeOOH sample is annealed in N2 at 350 DEG C for 2 h, and during the annealing process, the temperature rising rate is 2 DEG C / min. NaH2PO2 (1 g) and the FeOOH sample are respectively placed in the upstream and downstream of the tube furnace to obtain P-Fe3O4.

[0024] (4) The obtained P-Fe3O4 is immersed in a 0.4M NaBH4 solution at room temperature for 60 min, and then repeatedly washed with deionized water and alcohol and dried in a vacuum oven to obtain P-Fe3O4. 4-xThe synthesized material underwent morphological evolution, as shown in the scanning electron microscope image. Figure 2 ), P-Fe3O 4-x Densely interwoven nanosheets grow on the surface. Further characterization using TEM revealed a unique multilayer structure, consisting of numerous thin films. Figure 3 P-Fe3O 4-x The XRD results of the material are shown in the figure. Figure 4 The material is in the Fe3O4 phase, with P present as a dopant. (P-Fe3O) 4-x The electron paramagnetic resonance (EPR) signal indicates that unpaired electrons trapped by O vacancies on the material surface ( Figure 5 This confirmed the presence of O vacancies. During the HER electrocatalyst test (electrolyte: 1M KOH), only a working voltage of 294mV was required to reach 1Acm. -2 current density ( Figure 6 Subsequently, HER tests were also conducted in 1M KOH seawater electrolyte, achieving a 1Acm... -2 Only a 327mV operating voltage is required. Figure 7 It can operate stably for 1000 hours under industrial seawater conditions. Figure 8 The electrocatalyst prepared above exhibits excellent catalytic activity and stability, indicating that the synthesized P-Fe3O4... 4-x The catalyst shows promise for use in the electrolysis of alkaline seawater.

[0025] Example 2

[0026] A method for synthesizing P-doped O-vacancy self-supporting Fe3O4 for hydrogen production by seawater electrolysis includes the following steps:

[0027] (1) In this embodiment, 1cm*2cm foam iron is cut, and the foam iron is placed in hydrochloric acid, acetone and deionized water and sonicated for 30 minutes respectively. After vacuum drying, it is ready for use.

[0028] (2) Heat Fe(NO3)3·9H2O in an oven at 150℃ until it melts. Immerse the pretreated foamed iron in the molten salt and react for 40 minutes. Then, allow it to cool naturally to room temperature. Rinse repeatedly with deionized water and alcohol and dry in a vacuum oven.

[0029] (3) The FeOOH sample was annealed in N2 at 350℃ for 2.5h. The heating rate during the annealing process was 2℃ / min. NaH2PO2 (1g) and FeOOH sample were placed upstream and downstream of the tube furnace, respectively, to obtain P-Fe3O4.

[0030] (4) The obtained P-Fe3O4 was soaked in 0.4M NaBH4 solution at room temperature for 60 min, washed repeatedly with deionized water and ethanol, and dried in a vacuum oven to obtain P-Fe3O4. 4-x During the HER electrocatalyst test (electrolyte: 1M KOH), only 294mV of working voltage was required to achieve a current density of 1Acm -2 ( Figure 9 ).

[0031] Example 3

[0032] A synthesis method of P-doped O-vacancy self-supporting Fe3O4 for hydrogen production by electrolysis of seawater, comprising the following steps:

[0033] (1) In this embodiment, 1cm*2cm foamed iron was cut, and the foamed iron was placed in hydrochloric acid, acetone and deionized water for ultrasonic treatment for 30 min, and then dried in a vacuum oven for standby.

[0034] (2) Fe(NO3)3·9H2O was heated to melt at 150℃, and the pretreated foamed iron was immersed in the above molten salt for reaction for 30 min and then naturally cooled to room temperature. After washing repeatedly with deionized water and alcohol, it was dried in a vacuum oven.

[0035] (3) The FeOOH sample was annealed in N2 at 250℃ for 2h, and the heating rate during the annealing process was 2℃ / min. NaH2PO2 (1g) and FeOOH sample were placed in the upstream and downstream of the tube furnace, respectively, to obtain P-Fe3O4.

[0036] (4) The obtained P-Fe3O4 was soaked in 0.4M NaBH4 solution at room temperature for 60 min, washed repeatedly with deionized water and ethanol, and dried in a vacuum oven to obtain P-Fe3O4. 4-x .

[0037] This example explores that the series shielding effect reduces the adsorption energy of Cl - on the Fe active site of Fe3O4, effectively inhibits the toxicity of Cl - , and at the same time improves the activity and long-term stability of the catalyst.

[0038] The catalyst material prepared in this example can be applied in anion exchange membrane electrolytic cell Figure 10 , and can be stably operated for 100h Figure 11 under industrial seawater conditions. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 : Scanning electron microscope image of the precursor material obtained in Example 1

[0040] Figure 2 P-Fe3O obtained in Example 1 4-x Scanning electron microscope image

[0041] Figure 3 P-Fe3O obtained in Example 1 4-x Transmission electron microscope image

[0042] Figure 4 P-Fe3O obtained in Example 1 4-x X-ray diffraction pattern

[0043] Figure 5 P-Fe3O obtained in Example 1 4-x electron paramagnetic resonance image

[0044] Figure 6 P-Fe3O obtained in Example 1 4-x Hydrogen evolution performance in alkaline solution. The X-axis represents the operating potential (V), and the Y-axis represents the current density (A / cm²). -2 )

[0045] Figure 7 P-Fe3O obtained in Example 1 4-x Hydrogen evolution performance in alkaline seawater solution. The X-axis represents the operating potential (V), and the Y-axis represents the current density (A / cm²). -2 )

[0046] Figure 8 P-Fe3O obtained in Example 1 4-x Hydrogen evolution stability in alkaline seawater solution. The X-axis represents operating time (h), and the Y-axis represents current density (A / cm²). -2 )

[0047] Figure 9 P-Fe3O obtained in Example 2 4-x Hydrogen evolution performance in alkaline seawater solution. The X-axis represents the operating potential (V), and the Y-axis represents the current density (A / cm²). -2 )

[0048] Figure 10 The chronocurrent curves of the anion exchange membrane electrolyzer assembled in Embodiment 3 of this invention are shown. The X-axis represents the operating potential (V), and the Y-axis represents the current density (A / cm²). -2 )

[0049] Figure 11 The stability curve of the anion exchange membrane electrolyzer assembled in Example 3 of this invention is shown. The X-axis represents the operating time (h), and the Y-axis represents the operating potential (V).

[0050] The above merely provides the preferred embodiment of the present application, and not intended to limit the present application. Accordingly, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall fall within the scope of protection of the present application.

Claims

1. A method for preparing an electrolytic seawater catalyst for adjusting the local atomic environment by P-doping and oxygen vacancies, the steps of which are: simple cleaning treatment of a self-supporting material, and further heating Fe(NO3)3·9H2O to melting in a salt bath at 130-170 °C in an oven, immersing the pretreated iron foam into the above molten salt for 5-20 min, and then naturally cooling to room temperature, and then repeatedly washing with deionized water and alcohol, and then drying in a vacuum oven to obtain a FeOOH precursor, and then using phosphating calcination and reduction treatment in a NaBH4 solution to obtain a modified P-Fe3O4 catalyst. 4-x The electrocatalyst can efficiently produce hydrogen gas while maintaining long-term stability under the conditions of industrial seawater.

2. The method for preparing an electrolytic seawater catalyst by P-doping and oxygen vacancy to adjust local atomic environment according to claim 1, cutting the self-supporting material foam iron into appropriate size, respectively immersing in hydrochloric acid, acetone, deionized water, and ultrasonic treatment.

3. A method for the preparation of an electrolytic seawater catalyst by P-doping and oxygen vacancy adjustment of the local atomic environment according to claim 1, characterized in that, FeOOH samples are annealed in N2 at 300-400 ℃ for 1-3 h, 0.5-2 g of NaH2PO2 and FeOOH samples are respectively placed in the upstream and downstream of the tube furnace during the annealing process, and P-Fe3O4 is obtained.

4. A process for the preparation of an electrolytic sea water catalyst by P-doping and oxygen vacancy to adjust local atomic environment as claimed in claim 1, wherein the P-Fe304 obtained is soaked in 0.1-0.5 M NaBH4 solution for 30-90 min at room temperature, washed repeatedly with deionized water and ethanol and dried in a vacuum oven to obtain P-Fe304. 4-x .

5. The application of the catalyst prepared by the method for preparing an electrolytic seawater catalyst by P-doping and oxygen vacancy to adjust local atomic environment according to claim 1, the electro-catalyst can be applied as a cathode in an alkaline anion exchange membrane electrolyzer.

6. The application according to claim 5, using natural seawater to prepare an electrolyte of 1 M KOH, and keeping the electrolyte temperature at 60 °C during the electrolysis of seawater.

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