Preparation method and application of a ferric oxyhydroxide-metal organic framework heterostructure basic electrolytic water catalyst
By in-situ growing FeOOH and MOF-74 on a foamed iron substrate to form a heterogeneous electrocatalyst, the problems of high overpotential and poor stability of existing electrocatalysts are solved, achieving a highly efficient and durable electrocatalytic water splitting effect, which is suitable for electrocatalytic water splitting reactions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN UNIV OF TECH
- Filing Date
- 2023-03-24
- Publication Date
- 2026-06-19
AI Technical Summary
Existing electrocatalysts suffer from high overpotential and poor stability in water splitting reactions. In particular, the scarcity and high cost of precious metal catalysts limit their large-scale application. There is a need to develop efficient and durable bifunctional electrocatalysts to reduce overpotential and improve stability.
A two-step method involving constant current anodic oxidation and hydrothermal reaction using a three-electrode system was employed to in-situ convert FeOOH and uniformly grow MOF-74 on a foamed iron substrate, forming a FeOOH@MOF-74/IF heterostructure electrocatalyst. This method avoids high-temperature treatment and allows the catalyst to be directly used as the electrocatalytic electrode.
The prepared FeOOH@MOF-74/IF electrocatalyst exhibits a small overpotential and fast water splitting kinetics in alkaline electrolyte, with excellent high current stability and high active surface area, making it suitable for electrocatalytic water splitting reactions, especially showing significant catalytic advantages in OER and HER processes.
Smart Images
Figure CN116254574B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of electrochemical energy storage materials. The technology involves the preparation and post-processing methods of iron hydroxyl oxide (FeOOH) and metal-organic framework (MOF) composite materials. Based on the heterostructure of FeOOH@MOF-74 loaded on iron foam (IF), a highly active, highly stable and highly conductive electrocatalyst is obtained. Background Technology
[0002] Renewable energy-driven water splitting is one of the sustainable and feasible methods for producing green and clean hydrogen energy through water electrolyzers via the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. However, the slow kinetics and large overpotentials are two bottlenecks in both half-reactions. To overcome these bottlenecks, the development of efficient electrocatalysts is crucial and urgently needed. Currently, platinum-carbon (Pt-C) and ruthenium oxide (RuO2) / iridium oxide (IrO2) are the standard electrocatalysts for HER and OER, respectively. However, their scarcity, high cost, and lack of durability for long-term operation severely hinder their large-scale industrial application. Therefore, there is an urgent need to fabricate efficient and durable bifunctional electrocatalysts for HER and OER that can operate at lower overpotentials to reduce energy loss in the process. In this regard, through continuous efforts, earth-abundant transition metal-based materials with highly competitive bifunctional electrocatalytic activity have been synthesized, attracting widespread attention.
[0003] Metal-organic frameworks (MOFs) are a class of porous crystalline hybrid materials formed by the combination of metal ions or clusters with organic ligands, creating periodic structural units with well-defined metal centers and tunable morphologies. However, directly applying pristine MOFs to obtain catalytic activity results in drawbacks such as poor conductivity, slow charge transfer rates, and poor stability due to the direct binding of ligand molecules to the metal centers. To improve their catalytic cycle stability, MOFs have been modified, such as through calcination and etching to create porous derivatives, or by combining them with other inorganic materials to form superior structures that enhance charge transport and stability. Iron hydroxyl oxide (FeOOH), as a non-noble metal material, is considered an active center for water splitting reactions, exhibiting high activity and stability. Its heterostructure with MOFs promotes the water splitting process.
[0004] However, as a highly efficient and durable water splitting catalyst, reducing the overpotential of the reaction and improving its stability under high current remains a huge challenge for researchers. Summary of the Invention
[0005] Based on the technical problems mentioned above, the purpose of this invention is to provide a method for preparing FeOOH@MOF-74 / IF electrocatalyst that is simple in pretreatment, uses inexpensive and readily available raw materials, and has mild reaction conditions.
[0006] A method for preparing an alkaline water electrolysis catalyst with an iron hydroxyl oxide-metal-organic framework heterostructure involves a two-step process of constant current anodic oxidation and hydrothermal reaction in a three-electrode system. This process involves the in-situ conversion of FeOOH and the uniform growth of MOF-74 on an iron foam (IF) substrate, which is then directly used as the electrocatalytic reaction electrode.
[0007] The technical solution adopted in this invention is as follows:
[0008] A method for preparing an iron hydroxyl oxide-metal-organic framework heterostructure alkaline water electrolysis catalyst involves uniformly growing the FeOOH@MOF-74 / IF heterostructure electrocatalyst on a conductive substrate of iron foam via electrochemical anodic oxidation and solvothermal reaction. After being washed three times with alternating ethanol and deionized water and dried, the catalyst is directly used as the electrocatalytic electrode material.
[0009] Specifically, the following steps are included:
[0010] (1) Clean the conductive substrate foam iron supported on the catalyst and vacuum dry it;
[0011] (2) Take cleaned and dried foamed iron, cut it into a rectangle, and use it as the anode. Use Pt wire as the cathode and Hg / HgO as the reference electrode. In the electrolyte, the current density is 10-200 mA·cm. -2 Constant current anodic oxidation was performed to obtain FeOOH / IF;
[0012] The electrolyte contains 1-2M KOH solution, and the constant current oxidation time is 3-16h.
[0013] (3) 2,5-Dihydroxyterephthalic acid and nickel nitrate hexahydrate were dissolved in a mixed solvent of N,N-dimethylformamide / ethanol / deionized water and ultrasonically treated to obtain a homogeneous mixed solution.
[0014] The concentration of 2,5-dihydroxyterephthalic acid in the mixture is 0.01–0.1 M, and the concentration of nickel nitrate hexahydrate is 0.01–0.1 M.
[0015] (4) Transfer the mixed solution to a Teflon-lined stainless steel autoclave, tilt the conductive substrate treated with constant current into the autoclave, then seal the autoclave and keep it at 100-120°C for 12-36 hours.
[0016] (5) After the reaction is complete, the autoclave is naturally cooled, then removed, cleaned, and vacuum dried to obtain the electrocatalytic material.
[0017] The aforementioned electrocatalytic materials are applied to electrocatalytic water desorption / oxygen evolution / overall water splitting reactions.
[0018] Furthermore, the method specifically includes the following steps:
[0019] (1) Clean the conductive substrate foam iron and vacuum dry it;
[0020] (2) In the three-electrode system, foamed iron is used as the working electrode, platinum wire as the counter electrode, and Hg / HgO as the reference electrode, and a constant current (10~200mA·cm) is applied. -2 Anodizing, oxidation time 3-16h, followed by vacuum drying;
[0021] (3) 2,5-Dihydroxyterephthalic acid (H4DOBDC, 0.1-0.9 mmol) and nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.1-0.9 mmol) were mixed and dissolved in a mixed solvent of N,N-dimethylformamide / ethanol / deionized water and then ultrasonically treated.
[0022] (4) Transfer the mixed solution to a 15mL stainless steel high-pressure reactor lined with Teflon. The anodized IF is tilted into the high-pressure reactor. Then, the high-pressure reactor is sealed and kept at 100-120℃ for 12-36 hours.
[0023] (5) After the reaction is complete and the autoclave is cooled naturally, IF is taken out of the autoclave and rinsed repeatedly with deionized water and ethanol to remove impurities and weakly adsorbed catalyst.
[0024] (6) Dry the prepared sample in a vacuum drying oven at 60℃.
[0025] Furthermore, cut the foam iron into pieces with an area of 2 × 2.5 cm. 2 Thickness: 1.5 mm, and then sonicated in 1M HCl, acetone, deionized water and anhydrous ethanol for 15-30 minutes in sequence.
[0026] Furthermore, in a three-electrode system, foamed iron is used at current densities of 10–200 mA·cm⁻¹. -2 Anodize for 3-16 hours, then vacuum dry.
[0027] Furthermore, 2,5-dihydroxyterephthalic acid and nickel nitrate hexahydrate were dissolved in a prepared N,N-dimethylformamide / ethanol / deionized water (v / v / v = 50:3:3) mixed solvent (11.2 mL, 0.01–0.1 M) and sonicated for 20–30 minutes.
[0028] Furthermore, under hydrothermal conditions, the temperature is slowly increased and kept constant at 105°C for 12–36 hours.
[0029] Furthermore, the high-pressure reactor is naturally cooled to 20℃~40℃ in an oven. After being removed by tweezers, the front and back sides of the IF are repeatedly rinsed three times each with deionized water and ethanol to remove impurities and weakly adhered blocky catalysts.
[0030] Further, the rinsed IF is placed in a vacuum drying oven and dried at a constant temperature for 6 to 12 hours.
[0031] Furthermore, the ultrasonic frequency of the ultrasonic equipment used is 50–53 kHz.
[0032] This invention also provides a method for preparing the above-mentioned iron hydroxyl oxide-metal-organic framework heterostructure, in which the catalyst can be directly used as an electrocatalyst. In a standard three-electrode system (Hg / HgO as the reference electrode, platinum wire as the counter electrode and working electrode), the iron hydroxyl oxide-metal-organic framework electrocatalyst is placed directly as the working electrode in the electrolyte to perform electrocatalytic water desorption oxygen evolution (OER), hydrogen evolution reaction (HER), and total water splitting reaction (OWS).
[0033] Furthermore, the electrolyte described above is a prepared 1M KOH solution.
[0034] This invention employs a two-step method involving anodic oxidation and one-pot hydrothermal reaction. First, constant current anodic oxidation is performed to obtain pretreated IF. The pretreated IF, 2,5-dihydroxyterephthalic acid, and nickel nitrate hexahydrate are then thoroughly dissolved and homogenized in a Teflon stainless steel autoclave for heating and reaction to synthesize transition metal-based Ni-MOFs materials. This method eliminates the need for etching and high-temperature calcination, preserving the unique structure of the electrocatalytic material, and allows it to be directly used as a water splitting electrode.
[0035] Compared with the prior art, the present invention has the following advantages:
[0036] 1. The heterostructure electrocatalyst prepared by the present invention can be uniformly loaded on the substrate iron foam, grow in situ and bond firmly with the substrate, avoid the weak conductivity caused by the use of binders for drop coating, and can be used directly as an electrode material without high-temperature post-treatment.
[0037] 2. By constructing heterostructures through (electro)chemistry, the electronic structure and charge / mass transfer performance during the catalytic process can be optimized. The substrate is iron foam, which improves conductivity. Porous heterostructures typically expose more active sites, allowing the catalyst to exhibit significant advantages.
[0038] 3. Electrochemical performance is an important indicator for evaluating the quality of electrocatalysts. In an alkaline 1M KOH system, FeOOH@MOF-74 / IF at 10 mA·cm⁻¹... -2 and 100mA·cm -2 FeOOH@MOF-74 / IF exhibits smaller HER and OER overpotentials at a current density significantly better than other reference terms, and also shows a small Tafel slope, indicating fast water splitting kinetics. Compared to other reference terms, FeOOH@MOF-74 / IF has the largest active surface area and low impedance, accelerating the charge transfer process and thus the water splitting kinetics. FeOOH@MOF-74 / IF at 10 mA·cm⁻¹ exhibits these characteristics. -2 and 100mA·cm -2 It can remain stable for more than 120 hours under high current density. When FeOOH@MOF-74 / IF is used as both the cathode and anode for water splitting, a total water splitting electrolysis cell is assembled. It has a low cell voltage, indicating that it has good electrochemical activity and stability.
[0039] In summary, this invention provides a two-step method for preparing a three-dimensional self-supporting electrode through electrochemical anodic oxidation and one-pot hydrothermal synthesis. The method is simple and reproducible, requiring no cumbersome high-temperature pyrolysis or etching processes, and is easy to prepare on a large scale. The resulting material has significant advantages in catalyzing water splitting reactions and energy conversion. In OER and HER processes, the prepared heterostructure electrocatalyst has a very small overpotential and a very small potential during the total water splitting process, and it also exhibits excellent high-current electrochemical stability. Attached Figure Description
[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below.
[0041] Figure 1 The image shows the X-ray diffraction pattern of the heterostructure electrocatalyst FeOOH@MOF-74 / IF prepared by a two-step method.
[0042] Figure 2 The Fourier transform infrared spectrum of the heterostructure electrocatalyst FeOOH@MOF-74 / IF prepared by a two-step method is shown.
[0043] Figure 3 This is a scanning electron microscope (SEM) image of the heterostructured electrocatalyst FeOOH@MOF-74 / IF prepared by a two-step method.
[0044] Figure 4 The image shows the EDS spectrum of the heterostructure electrocatalyst FeOOH@MOF-74 / IF prepared by a two-step method.
[0045] Figure 5(a) shows the LSV curves of the oxygen evolution reaction (OER) of the heterostructured electrocatalyst FeOOH@MOF-74 / IF prepared by the two-step method and its comparative sample; (b) shows the Tafel slope of the OER of the heterostructured electrocatalyst FeOOH@MOF-74 / IF prepared by the two-step method and its comparative sample; (c) shows the active surface area of the OER of the heterostructured electrocatalyst FeOOH@MOF-74 / IF prepared by the two-step method and its comparative sample; and (d) shows the impedance diagram of the OER of the heterostructured electrocatalyst FeOOH@MOF-74 / IF prepared by the two-step method and its comparative sample.
[0046] Figure 6 The LSV curves of the hydrogen evolution reaction of the heterostructured electrocatalyst FeOOH@MOF-74 / IF prepared by the two-step method and its comparative sample are shown.
[0047] Figure 7 LSV curves of the total water splitting reaction of the heterostructured electrocatalyst FeOOH@MOF-74 / IF prepared by the two-step method and its comparative sample.
[0048] Figure 8 It test of the heterostructured electrocatalyst FeOOH@MOF-74 / IF prepared by the two-step method.
[0049] Figure 9 LSV curves of oxygen evolution reaction before and after itinerary test for FeOOH@MOF-74 / IF.
[0050] Figure 10 X-ray diffraction pattern of FeOOH@MOF-74 / IF after OER reaction.
[0051] Figure 11 Scanning electron microscope image of FeOOH@MOF-74 / IF after OER reaction. Detailed Implementation
[0052] To make the present invention concise and easy to understand, the following embodiments are preferred, and detailed descriptions are provided in conjunction with the accompanying drawings. Unless otherwise specified, all raw materials are available from publicly available commercial sources.
[0053] Example 1: Preparation of an alkaline water electrolysis catalyst with a hydroxyl iron oxide-metal-organic framework heterostructure
[0054] Foam iron (IF) (area: 2×2.5cm) 2 (Thickness: 1.5mm) was sequentially immersed in 1M HCl, acetone, deionized water and anhydrous ethanol and sonicated for 30 minutes to remove weakly adsorbed impurities on the surface.
[0055] Keep IF in a vacuum drying oven at 60°C for 6 hours to keep the foamed iron dry and prevent it from being oxidized;
[0056] Using foamed iron as the working electrode, Pt wire as the counter electrode, Hg / HgO as the reference electrode, and 1M KOH as the electrolyte, a constant current of 100 mA·cm⁻¹ was applied in a three-electrode system. -2 After 8 hours, the sample was removed and rinsed three times with anhydrous ethanol to obtain FeOOH / IF, which was then dried in a vacuum drying oven at 60°C for 6 hours.
[0057] 2,5-Dihydroxyterephthalic acid (H4DOBDC, 0.3 mmol) and nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.9 mmol) were dissolved in a mixed solvent of N,N-dimethylformamide / ethanol / deionized water (11.2 mL, v / v / v = 50:3:3) and sonicated for 30 minutes until completely dissolved.
[0058] The mixed solution was quickly transferred to a 15 mL stainless steel autoclave lined with Teflon, and the FeOOH / IF was tilted and placed into the autoclave.
[0059] The high-pressure reactor was sealed and slowly heated to 105°C at a heating rate of 2°C / min, and then kept at 105°C for 24 hours before being allowed to cool naturally to room temperature.
[0060] The IF was removed from the high-pressure reactor and rinsed three times on both sides with deionized water and ethanol respectively to remove weakly adsorbed catalyst and impurities.
[0061] The obtained sample was kept under vacuum at 60°C for 12 hours.
[0062] Comparative example FeOOH / IF
[0063] Using the method of Example 1, only the IF is subjected to a constant current of 100mA·cm. -2 Anodizing for 8 hours, without loading MOF-74 using the hydrothermal method.
[0064] Comparative example MOF-74 / IF
[0065] Using the method of Example 1, only the IF was not subjected to anodic constant current anodizing treatment, and MOF-74 was directly loaded on it by hydrothermal method.
[0066] Example 2: Application of water electrolysis catalyst
[0067] The application of the hydroxyl iron oxide-metal-organic framework heterostructure alkaline water electrolysis catalyst from Example 1 to the electrocatalytic water splitting processes OER, HER, and OWS is as follows:
[0068] (1) Preparation of working electrode
[0069] Cut the prepared dried FeOOH@MOF-74 / IF into 1×2cm pieces. 2 Used directly as the working electrode;
[0070] (2) Electrocatalytic oxygen evolution and hydrogen evolution reactions
[0071] All electrochemical tests were performed in a three-electrode system at room temperature, using a Pt wire as the counter electrode, a Hg / HgO electrode as the reference electrode, and the prepared catalyst and control sample as the working electrodes. 1M KOH was used as the electrolyte for all electrochemical tests. Before the electrochemical OER and HER tests, the electrodes were activated by CV (CV) for 10 cycles at a scan rate of 50 mV·s. -1 .
[0072] (3) Electrocatalytic total water splitting reaction
[0073] Using the OER and HER methods, only the counter electrode Pt wire was replaced with FeOOH@MOF-74 / IF.
[0074] Example 3
[0075] (1) Characterization of FeOOH@MOF-74 / IF catalytic reaction before reaction
[0076] from Figure 1 The XRD pattern shows that the crystal structure of FeOOH@MOF-74 / IF indicates that the synthesized FeOOH / IF can be well classified as iron hydroxyoxide (PDF#08-0098). Compared with FeOOH / IF, the XRD diffraction pattern of FeOOH@MOF-74 / IF shows several new characteristic peaks at 14.1° and 44.6°, which is very consistent with the XRD pattern of pure MOF-74 and can be attributed to the MOF (CCDC No. 288477) constructed from nickel ions and H4DOBDC ligands. Figure 2 In the spectroscopy, H4DOBDC and MOF-74 were characterized using Fourier transform infrared (FT-IR) spectroscopy. The range was 3000–3200 cm⁻¹. -1 The frequency band was allocated as υ OH , and 1644cm -1 υ assigned as H4DOBDC C＝O In MOF-74, the stretching of OH and C=O completely disappears, indicating successful coordination of carboxyl and hydroxyl groups with nickel. Combined with these results, this strongly demonstrates the successful preparation of FeOOH@MOF-74 on foamed iron. Figure 3 In scanning electron microscopy (SEM), MOF-74 with a flower-like nanoarray structure is uniformly covered on the FeOOH / IF surface. Figure 4Elemental analysis revealed that C, O, Fe, and Ni elements were uniformly distributed in the FeOOH@MOF-74 / IF electrocatalyst.
[0077] (2) Electrochemical testing of FeOOH@MOF-74 / IF
[0078] The electrochemical performance of an electrocatalyst is an important indicator for evaluating its quality. Figure 5 As shown in (a), the LSV of the oxygen evolution reaction indicates that FeOOH@MOF-74 / IF at 10 mA·cm⁻¹ -2 and 100mA·cm -2 The overpotentials were 188 and 234 mV, respectively, which were significantly better than the reference terms (FeOOH / IF, MOF-74 / IF, and IF). In (b), FeOOH@MOF-74 / IF had the smallest Tafel slope of 17.3 mV·dec. -1 The results indicate that it has relatively fast OER kinetics. In (c) and (d), FeOOH@MOF-74 / IF has a large active surface area and low impedance, demonstrating the fast electron transfer process of the heterostructure electrocatalyst and exhibiting good OER activity. Figure 6 In the LSV of the hydrogen evolution reaction, at 100 mA·cm -2 The overpotential is 268mV, which shows better hydrogen evolution activity than the reference term. Figure 7 The FeOOH@MOF-74 / IF||FeOOH@MOF-74 / IF full-cell electrolyzer, composed of these components, can achieve 100 mA·cm⁻¹ with only 1.50 V. -2 It has potential for industrialization. Figure 8 and Figure 9 In the study, FeOOH@MOF-74 / IF demonstrated excellent stability at high current densities, and after 100 mA·cm⁻¹... -2 After stability testing (120 h), the electrochemical performance did not decrease significantly, indicating its potential application value as a hydrogen production electrocatalyst.
[0079] (3) Characterization of FeOOH@MOF-74 / IF after electrochemical testing
[0080] from Figure 10 and Figure 11 The X-ray diffraction pattern and scanning electron microscope showed that after the electrochemical high current stability test, the structure and morphology of FeOOH@MOF-74 / IF changed significantly. The crystal structure of FeOOH and MOF disappeared and was transformed into an amorphous Ni(Fe)OOH plate-like stacked structure, indicating that it is a true active species of electrocatalyst and has excellent electrochemical stability.
[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for preparing an alkaline water electrolysis catalyst with a hydroxyl iron oxide-metal-organic framework heterostructure, characterized in that, FeOOH@MOF-74 / IF heterostructure electrocatalysts were uniformly grown on conductive iron foam substrates via electrochemical anodic oxidation and solvothermal reaction. After being cleaned and dried with alternating ethanol and deionized water, the catalysts were directly used as electrocatalytic electrode materials. Specifically, the following steps are included: (1) Clean the conductive substrate foam iron supported on the catalyst and vacuum dry it; (2) Take cleaned and dried foamed iron, cut it into a rectangle, use it as the anode, use Pt wire as the cathode, and use Hg / HgO as the reference electrode. In the electrolyte, the current density is 10~200 mA·cm. -2 Constant current anodic oxidation was performed to obtain FeOOH / IF; The electrolyte contains 1-2 M KOH solution, and the constant current oxidation time is 3-16 h; (3) 2,5-Dihydroxyterephthalic acid and nickel nitrate hexahydrate were dissolved in a mixed solvent of N,N-dimethylformamide / ethanol / deionized water and ultrasonically treated to obtain a homogeneous mixed solution; The concentration of 2,5-dihydroxyterephthalic acid in the mixture is 0.01~0.1 M, and the concentration of nickel nitrate hexahydrate is 0.01~0.1 M. (4) Transfer the mixed solution to a Teflon-lined stainless steel autoclave, tilt the conductive substrate treated with constant current into the autoclave, then seal the autoclave and keep it at 100~120 ℃ for 12~36 hours; (5) After the reaction is complete, the autoclave is naturally cooled, then removed, cleaned, and vacuum dried to obtain the electrocatalytic material.
2. The electrocatalytic material prepared by the preparation method according to claim 1 is applied to electrocatalytic water desorption oxygen, hydrogen evolution, or overall water splitting reactions.