Catalyst for seawater electrolysis, and preparation method therefor and use thereof
By growing NiFe-MOF nanosheet arrays and depositing Ni3S4 nanoparticles on a nickel foam substrate to form a heterostructure catalyst, the problem of catalyst corrosion in seawater electrolysis was solved, the catalytic activity and stability were improved, the ion diffusion capacity was enhanced, and efficient seawater electrolysis was achieved.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- QINGDAO INST OF BIOENERGY & BIOPROCESS TECH CHINESE ACADEMY OF SCI
- Filing Date
- 2024-12-25
- Publication Date
- 2026-06-18
AI Technical Summary
Existing catalysts are easily corroded by high concentrations of Cl- during seawater electrolysis, leading to poisoning of active sites and structural instability, which affects catalytic activity and lifespan. In addition, they have poor ion diffusion capacity, which reduces electrolysis efficiency.
A NiFe-MOF nanosheet array was grown on a nickel foam substrate and Ni3S4 nanoparticles were deposited. A heterogeneous structure was formed through sulfidation treatment, which enhanced the catalyst's resistance to chloride ion corrosion and structural stability.
The catalyst exhibits improved OER performance and stability in seawater electrolysis, increased catalytic active sites, enhanced ion diffusion capacity, reduced overpotential, and no significant structural changes after electrochemical testing, demonstrating excellent resistance to chloride ion corrosion and high stability.
Smart Images
Figure CN2024142389_18062026_PF_FP_ABST
Abstract
Description
A catalyst for seawater electrolysis, its preparation method and application
[0001] Cross-reference to related applications
[0002] This invention claims priority to Chinese Patent Application No. 202411830420.2, filed on December 12, 2024, entitled "A catalyst for electrolysis of seawater and its preparation method and application", the entire contents of which are incorporated herein by reference and constitute a part of this invention for all purposes. Technical Field
[0003] This invention belongs to the field of water electrolysis technology, specifically relating to a catalyst for seawater electrolysis, its preparation method, and its application. Background Technology
[0004] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
[0005] Electrochemical water splitting can produce high-purity hydrogen with high energy density and zero carbon emissions, and is considered a sustainable strategic technology for addressing global energy demand and mitigating environmental degradation. Currently, electrolytes from freshwater supplies are widely used for water splitting, but large-scale water splitting inevitably places a significant burden on scarce freshwater resources. Given the abundance of global seawater resources, direct seawater separation for hydrogen production has the potential to alleviate freshwater shortages and is therefore attracting increasing attention. However, high concentrations of ions (approximately 0.5 M) in seawater can trigger a competitive chloride evolution reaction (ClER) in the oxygen evolution electrolyte (OER) to form hypochlorite (ClO₂). - This leads to the corrosion of active sites, and high concentrations of Cl... - It is highly corrosive, poisoning metal active sites and accelerating catalyst aging, leading to a decrease in catalyst activity. Although OER exhibits a more favorable thermodynamic advantage than ClER under alkaline conditions (approximately 480 mV, pH > 7.5), ClER, involving two-electron transfer, has faster reaction kinetics than OER. This necessitates creating a suitable potential window (overpotential < 480 mV) for OER selectivity in alkaline seawater electrolytes. On the other hand, the deposition of insoluble precipitates [Ca(OH)2 and Mg(OH)2] during seawater oxidation inevitably leads to the poisoning of active sites, reducing catalyst lifetime. Therefore, to achieve high seawater electrolysis efficiency at high current densities, it is even more necessary to construct advanced catalysts with corrosion resistance and high activity.
[0006] Metal-organic frameworks (MOFs) are a class of porous network coordination polymers formed by coordination reactions between metal clusters / ions and organic ligands. They possess advantages such as ultra-high porosity, large specific surface area, and tunable structure and function, exhibiting high activity and strong adsorption capacity in water electrolysis. These unique properties make MOFs a promising catalyst and have attracted widespread attention for promoting water / seawater oxidation. Professor Huang Minghua's research group successfully prepared a NiFe-MOF@NiS heterojunction catalyst on a nickel foam substrate by growing crystalline NiS nanosheets on a nickel foam substrate using a sulfur-temperature modified corrosion method. Subsequently, amorphous NiFe-MOF nanoparticles were grown on the NiS surface through electrodeposition. (Xianbiao Hou, Chen Yu, Tengjia Ni, Shucong Zhang, Jian Zhou, Shuixing Dai, Lei Chu, Minghua Huang. Constructing amorphous / crystalline NiFe-MOF@NiS heterojunction catalysts for enhanced water / seawater oxidation at large current density[J]. Chinese Journal of Catalysis, 2024, 61: 192-204.) The inventors found that the MOF structure of this catalyst is restructured after OER, forming hydroxyl oxides, which have poor stability and are easily destroyed by high concentrations of Cl in seawater. - Corrosion and poisoning of catalytic sites. Simultaneously, its poor ion diffusion ability reduces charge transport efficiency at the interface, necessitating further improvement in catalytic activity. Summary of the Invention
[0007] To address the shortcomings of existing technologies, the present invention aims to provide a catalyst for seawater electrolysis, its preparation method, and its application. The catalyst provided by the present invention has excellent structural stability and more surface active sites.
[0008] To achieve the above objectives, the technical solution of the present invention is as follows:
[0009] A first aspect of the present invention provides a catalyst for the electrolysis of seawater, comprising:
[0010] Nickel foam substrate material;
[0011] An array of metal-organic framework nanosheets grown on the surface of the nickel foam substrate material, wherein the metal-organic framework contains nickel and iron;
[0012] A sulfide layer deposited on the surface of the metal-organic framework nanosheet array, the sulfide layer comprising Ni3S4 nanoparticles.
[0013] In some embodiments of the present invention, the metal-organic framework is formed by the free assembly of organic ligand NH2BDC with nickel and iron ions.
[0014] In some embodiments of the present invention, the metal-organic framework nanosheet array is flower-shaped, and the metal-organic framework nanosheet array forms a composite heterostructure with Ni3S4 nanoparticles deposited thereon.
[0015] A second aspect of the present invention provides a method for preparing the catalyst for seawater electrolysis, comprising the following steps:
[0016] Using NH2BDC as an organic ligand, nickel and iron salts as metal salts, and nickel foam as a substrate material, a hydrothermal reaction was carried out in an alkaline environment to grow a metal-organic framework nanosheet array on the surface of nickel foam.
[0017] Nickel foam with metal-organic framework nanosheet arrays grown on its surface was immersed in a sulfur source solution and subjected to a solvothermal reaction to obtain a catalyst for seawater electrolysis.
[0018] In some embodiments of the present invention, the nickel foam is pretreated before undergoing hydrothermal reaction to remove surface oxides and impurities.
[0019] In some embodiments of the present invention, NH2BDC is dissolved in a mixed solution, nickel salt and iron salt are added, the mixture is stirred to make it homogeneous, then an alkaline solution is added, and after mixing, nickel foam is introduced into the resulting solution for hydrothermal reaction. After the reaction is completed, the temperature is lowered to room temperature, and the product is washed and dried to obtain nickel foam with a metal-organic framework nanosheet array grown on the surface.
[0020] In some embodiments of the present invention, the mixed solution is obtained by mixing N,N-dimethylformamide, ethanol and water in a volume ratio of (14-18):1:1.
[0021] In some embodiments of the present invention, the nickel salt includes, but is not limited to, nickel nitrate, nickel chloride, or nickel sulfate.
[0022] In some embodiments of the present invention, the iron salt includes, but is not limited to, ferric nitrate, ferric chloride, or ferric sulfate.
[0023] In some embodiments of the present invention, the molar ratio of NH2BDC, nickel salt and iron salt is (1.2-1.3):(1-1.1):(0.2-0.3); and the concentration of NH2BDC in the mixed solution is 0.03-0.04 mol / L.
[0024] In some embodiments of the present invention, the concentration of the alkaline solution is 0.3-0.5M, and the volume ratio of the alkaline solution to the mixed solution is (0.9-1.1):(17-19).
[0025] In some embodiments of the present invention, the hydrothermal reaction is carried out at a temperature of 130–150°C for a time of 10–15 hours.
[0026] In some embodiments of the present invention, the sulfur source includes, but is not limited to, thioacetamide, thiourea, or sodium sulfide;
[0027] The solvent of the sulfur source solution is an alcohol compound, preferably ethanol; the concentration of the sulfur source in the sulfur source solution is 0.2-0.3 mol / L.
[0028] In some embodiments of the present invention, the solvothermal reaction is carried out at a temperature of 110–130°C and for a reaction time of 1–12 h, preferably 1–11 h, and more preferably 6 h.
[0029] A third aspect of the present invention provides a method for electrolyzing water, wherein the catalyst used in the electrolysis process is the catalyst described above or the catalyst prepared by the preparation method described above.
[0030] In some embodiments of the present invention, the water is seawater.
[0031] The beneficial effects of this invention are as follows:
[0032] This invention synthesizes a MOF-based electrocatalyst with excellent resistance to chloride ion corrosion, stability, and high controllability through a simple, rapid, and efficient sulfidation process for use in the OER reaction of seawater electrolysis. The OER performance of this catalyst at a current density of 100 mA cm⁻¹ -2 At this point, its overpotential was 292 mV, indicating high catalytic activity. Furthermore, after electrochemical testing, only Ni3S4 underwent reconstruction to form SO42- anions, while NiFe-MOF showed no significant oxidation or structural changes, demonstrating its good structural stability. Simultaneously, the SO42- anions preferentially adsorbed onto Fe4+ at the heterogeneous interface. 3+ Up, and then regulate the nearby Ni 2+ The electronic structure of Ni was optimized. 2+ The catalyst exhibits strong adsorption and desorption capabilities for OER reaction intermediates. Furthermore, after forming a heterogeneous interface between NiFe-MOF and Ni3S4 and conducting electrochemical tests, the concentrations of metallic Ni and Fe ions in the solution significantly decreased, demonstrating the catalyst's excellent structural stability and abundant surface active sites.
[0033] This invention provides a simple, efficient, and stable synthesis method for synthesizing metal-organic framework (MOF) catalysts with excellent chloride ion corrosion resistance and high stability through sulfidation treatment. The heterostructure formed by MOF and sulfides can alter the surface properties of the catalyst, thereby adjusting its chloride corrosion resistance and selectivity. This provides the possibility of customizing catalysts to suit specific reaction conditions. Furthermore, the sulfidation conditions can be adjusted by controlling the sulfidation time and temperature to achieve surface sulfidation of the MOF structure, constructing a heterostructure with a high specific surface area, which helps improve the ion diffusion capacity of the catalyst. This has significant practical implications for promoting the development of clean energy conversion devices, such as seawater electrolyzers, metal-air batteries, and fuel cells. Attached Figure Description
[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0035] Figure 1 is an electron microscope image of the material obtained in Example 1 of the present invention, wherein (a) and (b) are scanning electron microscope images of NiFe-MOF / NF at different magnification sizes, (c) is a scanning electron microscope image of NiFe-S-6h-MOF / NF, and (d) is a transmission electron microscope image of NiFe-S-6h-MOF / NF.
[0036] Figure 2 shows the (a) XRD pattern, (b) Raman spectrum, (c) XPS full spectrum of NiFe-S-6h-MOF / NF obtained in Example 1 of the present invention; (d)-(g) are the high-resolution XPS spectra of NiFe-MOF / NF and NiFe-S-6h-MOF / NF: (d) O 1s, (e) Ni 2p, (f) Fe 2p, (g) S2p;
[0037] Figure 3 shows the XPS spectra of the NiFe-S-6h-MOF / NF catalyst obtained in Example 1 of this invention before and after electrochemical testing in 1M KOH alkaline seawater solution, where (a) O 1s; (b) Ni 2p; (c) Fe 2p; (d) S 2p;
[0038] Figure 4 shows the relevant performance of the NiFe-S-6h-MOF / NF catalyst obtained in Example 1 of the present invention. Among them, (a) is the Raman spectrum of the NiFe-S-6h-MOF / NF catalyst after electrochemical testing; (b) is the relationship between the amount of various anions and the distance above the electrode surface in the classical molecular dynamics simulation of the electrolyte system above the electrode surface; and (c) is the ion chromatography of the NiFe-S-6h-MOF / NF solution after stability testing in 1M KOH + 0.5M NaCl electrolyte.
[0039] Figure 5 shows the OER performance of the material obtained in Example 1 of the present invention in simulated seawater with different NaCl concentrations. (a) is NiFe-MOF / NF, and (b) is NiFe-S-6h-MOF / NF.
[0040] Figure 6 shows the OER performance comparison between NiFe-S-6h-MOF / NF obtained in Example 1 of this invention and other control catalysts, where (a) is the LSV curve; (b) is the Tafel plot; (c) is the Nyquist plot; (d) is the TOF and MA plots; (e) is the Cdl plot; and (f) is the current density of NiFe-S-6h-MOF / NF in 1M KOH seawater at 100 mA cm⁻¹. -2 Long-term stability test chart. Detailed Implementation
[0041] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.
[0042] Example 1
[0043] The synthesis of a NiFe-S-MOF / NF catalyst for seawater electrolysis includes the following steps:
[0044] 1. Pretreatment of nickel foam: Cut nickel foam (NF) into 2cm*4cm pieces. In order to remove oxides and organic impurities, ultrasonically treat with 5M HCl, anhydrous ethanol and deionized water for 15 minutes in sequence, and then dry for later use.
[0045] 2. Accurately weigh 1.25 mmol (226.4 mg) of NH2BDC using a high-precision electronic balance and place it in a clean beaker containing a magnetic rotor. Use a pipette to measure 32 mL of N,N-dimethylformamide (DMF), 2 mL of ethanol, and 2 mL of deionized water and add them to the beaker. Seal the beaker with plastic wrap and stir the solution with a magnetic stirrer at 700 r / min for 10 min to ensure it is fully dissolved.
[0046] 3. Weigh 1.04 mmol (302.4 mg) Ni(NO3)2·6H2O and 0.26 mmol (105 mg) Fe(NO3)3·9H2O using a high-precision electronic balance and add them to the solution obtained in step 2. Stir magnetically at 700 r / min for 10 min to ensure the solution is mixed evenly.
[0047] 4. Use a pipette to measure 2 mL of 0.4 M NaOH aqueous solution and add it to the solution obtained in step 3. Stir magnetically at 700 r / min for 10 min to ensure the solution is mixed evenly.
[0048] 5. After stirring evenly, transfer the solution obtained in step 4 to the liner of a 50 mL reactor. Immerse the pretreated NF from step 1 into the solution, seal the autoclave, and maintain it at 140 °C for 12 hours (heating rate of 1 °C / min). Cool to room temperature with the furnace, thoroughly wash the product with ethanol and deionized water, and then dry it in a vacuum drying oven at 50 °C to obtain NiFe-MOF@NF.
[0049] 6. Weigh 2.66 mmol (199.8 mg) of thioacetamide (TAA) into a clean beaker with a magnetic stir bar using a high-precision electronic balance. Add 10 mL of anhydrous ethanol to the beaker using a pipette, and then stir magnetically at 700 r / min for 10 min. After the solution is stirred evenly, transfer it to the liner of a 50 mL reaction vessel.
[0050] 7. Cut the NiFe-MOF@NF obtained in step 5 into two pieces with a size of 2cm*2cm, immerse them in the solution obtained in step 6, seal the autoclave and keep them at 120℃ for 1h, 6h and 12h respectively (the temperature is raised from room temperature to the target temperature within 30min), cool them naturally to room temperature, wash them with ethanol and deionized water, and dry them. The catalysts prepared are represented as NiFe-S-1h-MOF / NF, NiFe-S-6h-MOF / NF and NiFe-S-12h-MOF / NF respectively.
[0051] Experimental Example
[0052] 1. Morphological characteristics
[0053] Scanning electron microscopy (SEM) (Figure 1(a), (b), and (c)) shows that NiFe-MOF / NF exhibits a flower-like structure assembled from nanosheets (approximately 50 nm thick). After sulfurization, granular material is uniformly grown on the surface of the nanosheets. Transmission electron microscopy (TEM) (Figure 1(d)) shows that urchin-like nanoparticles are distributed on the NiFe-S-6h-MOF / NF nanosheets.
[0054] The X-ray diffraction pattern (Figure 2(a)) shows that characteristic peaks of Ni3S4 appear with increasing sulfidation time, indicating the formation of a heterostructure. This unique structure endows the catalyst with a larger surface area and more accessible reactive sites, and effectively promotes the diffusion of electrolyte solution and the dissipation of bubbles. Simultaneously, the interfacial coupling and synergistic effect between Ni3S4 and NiFe-MOF can reduce the adsorption energy of reaction intermediates and promote rapid charge transport on the catalyst surface.
[0055] Raman spectra (Figure 2(b)) show that the characteristic peaks corresponding to the carboxylate groups gradually broaden with increasing sulfidation time, indicating that the MOF structure underwent a crystallization process under the sulfidation strategy. When the sulfidation time reaches 12 h, the characteristic peaks almost completely disappear, at which point the MOF is completely converted into sulfides.
[0056] The X-ray photoelectron spectroscopy (XPS) (Figure 2(e)) shows that after sulfidation, the peak of divalent nickel shifts to a lower binding energy, indicating a change in electronic structure. This is due to the introduction of low electronegativity S atoms, which brings adjacent Ni atoms into an electron-rich state. This is beneficial for improving charge transfer efficiency, thereby enhancing its catalytic efficiency. The positive shift of the Fe 2p peak is attributed to the formation of Fe-S bridging units (Figure 2(f)). The S2p spectrum (Figure 2(g)) shows the presence of sulfide anions and sulfate groups generated by the oxidation of surface sulfur species.
[0057] 2. High controllability
[0058] Sulfidation conditions can be adjusted by modifying the sulfidation time and temperature to achieve surface sulfidation of the MOF structure, constructing a heterogeneous interface with a high specific surface area, which helps improve the ion diffusion capacity in the catalyst. This invention, through sulfidation treatment, precisely induces the coating of controllable Ni3S4 nanoparticles on the surface of the NiFe-S-6h-MOF / NF catalyst, reducing the electronic valence state of the nickel sites on the catalyst surface and regulating the electronic structure of the active sites. This improves ion diffusion kinetics, thereby promoting the adsorption and desorption of OER reaction intermediates. Simultaneously, NiFe-MOF gradually becomes amorphous during sulfidation. Compared to crystalline MOFs, amorphous MOFs have abundant defect sites and unpaired electrons on their surface. Their more frequent orbital coupling leads to the redistribution of local lone pairs of electrons, accelerating charge transfer between active sites and the electrolyte.
[0059] 3. Structural stability
[0060] After electrochemical activation, only Ni3S4 underwent electrochemical reconstruction to form SO42- anions, while NiFe-MOF did not experience surface oxidation or structural changes, demonstrating the structural stability of the MOF. For the NiFe-MOF catalyst, after electrochemical testing, the concentrations of metallic Ni and Fe ions in the solution were 0.361 ppm and 0.384 ppm, respectively. After forming a heterogeneous interface between NiFe-MOF and Ni3S4 and performing electrochemical testing, the concentrations of metallic Ni and Fe ions in the solution significantly decreased to 0.087 ppm and 0.038 ppm, respectively. This indicates that the NiFe-S-6h-MOF / NF catalyst prepared in this invention possesses excellent structural stability and a greater number of surface active sites.
[0061] 4. Resistance to chloride ion corrosion
[0062] This invention constructs a heterostructure of MOF and transition metal sulfides through sulfidation treatment. During the electrochemical process, the sulfides generate SO₄²⁻ anions. These anions compete with chloride ions for adsorption, repelling chloride ions and preventing ClER (Cl-induced corrosion reaction), thus protecting the internal MOF structure from seawater corrosion. Furthermore, according to Pearson's hard-soft acid-base (HSAB) theory, SO₄²⁻ anions readily adsorb onto Fe²⁺. 3+ Furthermore, the activity of Ni can be adjusted. 2+ The electronic structure of the site promotes Ni 2+ Adsorption of *OH intermediate.
[0063] 5. Catalytic performance testing
[0064] Figure 3 shows a comparison of the XPS spectra of the NiFe-S-6h-MOF / NF catalyst before and after the electrochemical test in a 1M KOH alkaline seawater solution. The X-ray photoelectron spectroscopy (XPS) spectrum shows that after the electrochemical test, the peaks of iron (Figure 3(a)) and nickel (Figure 3(b)) shifted to lower binding energies, indicating that the catalyst surface underwent electron rearrangement after the electrochemical test, and the metal Ni and Fe sites were not oxidized, demonstrating that the MOF structure may have good stability. Simultaneously, the sulfur peak (Figure 3(d)) shifted to higher binding energies, the O 1s peak (Figure 3(c)) underwent a negative shift, and the corresponding SO bond peak broadened, indicating the formation of sulfate anions. These results indicate that charge transfer occurs from the sulfide nanoparticles to the Ni and Fe metal active centers on the NiFe-MOF, adjusting them to an electron-rich state, and simultaneously regulating the adsorption behavior of the Ni sites for the *OH intermediate, thereby accelerating the OER reaction kinetics. As shown in Figure 4(a), the structure of NiFe-MOF did not change significantly before and after the electrochemical test, further proving the structural stability of MOF.
[0065] The relationship between the amount of various anions and the distance above the electrode surface was simulated using classical molecular dynamics of the electrolyte system above the electrode surface. The simulation results are shown in Figure 4(b). The ion chromatography of the NiFe-S-6h-MOF / NF solution after stability testing in 1M KOH + 0.5M NaCl electrolyte is shown in Figure 4(c). The molecular dynamics simulation (Figure 4(b)) shows that without sulfate anions, chloride anions tend to accumulate above the electrode surface. After introducing sulfate into the electrolyte, divalent sulfate anions preferentially adsorb onto Fe2+ on the electrode surface. 3+ The resulting electrostatic repulsion can reduce Cl - Pushed away from the electrode surface. Figure 4(b) shows the distribution of various anions above the anode surface. Clearly, the presence of sulfate makes Cl... - It is difficult to access the electrode surface. Compared with the sulfate-free system, Cl within 1 nm of the surface is more abundant. - The content decreased by approximately half. Simultaneously, the introduction of sulfate anions reduced the OH- ions on the electrode surface. - The amount did not change significantly (Figure 4(b)), indicating that the additional SO4 2- This does not affect OER activity. Ion chromatography in Figure 4(c) further confirms the formation of sulfate ions in the electrochemical test. These results indicate that the sulfate ions formed on the catalyst surface can repel chloride ions from seawater without affecting the adsorption of surface-active intermediates; that is, OER activity is not affected while preventing chloride ion corrosion.
[0066] The OER performance of NiFe-S-6h-MOF / NF in simulated seawater with different NaCl concentrations was studied. The results showed that as the NaCl concentration increased, the LSV curve of NiFe-S-6h-MOF / NF (Figure 5(b)) showed a smaller change compared with NiFe-MOF / NF (Figure 5(a)), which once again proved that the presence of sulfate ions can improve the catalyst's resistance to chloride ion corrosion.
[0067] Therefore, this invention provides a simple, efficient, and stable synthesis method for synthesizing metal-organic framework catalysts with excellent resistance to chloride ion corrosion and high stability through sulfidation treatment. This has significant practical implications for promoting the development of clean energy conversion devices, such as seawater electrolyzers, metal-air batteries, and fuel cells.
[0068] 6. Electrochemical OER / HER performance
[0069] The electrochemical OER / HER performance of different MOF catalysts prepared in Example 1 was tested in a standard three-electrode system under ambient temperature and pressure. 1M KOH alkaline seawater was used as the electrolyte, the prepared MOF catalyst as the working electrode, a carbon rod as the counter electrode, and Hg / HgO as the reference electrode. All tests were conducted on a Chenhua 760 system. The results are shown in Figure 6.
[0070] In a 1M KOH alkaline seawater solution, the NiFe-S-6h-MOF / NF catalyst-modified electrode exhibited the best oxygen evolution catalytic activity (Figure 6(a)). At a current density of 100 mA cm⁻¹ -2 At this time, the overpotential is 292 mV, which is superior to the catalytic activity of commercial RuO2. This indicates that the long-range disordered structure formed by the amorphization of MOFs during sulfidation can endow MOFs with more active sites and a faster charge transfer rate, effectively improving the OER activity of the catalyst. The corresponding minimum Tafel slope (Figure 6(b)) is 94.5 mV dec. -1 This indicates that NiFe-S-6h-MOF / NF has a faster OER reaction kinetics.
[0071] Meanwhile, the NiFe-S-6h-MOF / NF catalyst showed the lowest charge transfer resistance (Figure 6(c)), indicating that NiFe-S-6h-MOF / NF possesses good electrical conductivity. This suggests that the reduction in charge transfer resistance after sulfidation treatment means that electrons are more easily transferred between catalyst surfaces. This helps improve the efficiency of electron transfer in the catalytic reaction, thereby promoting the rate at which the catalyst participates in the reaction. Simultaneously, the low charge transfer resistance reduces electron loss at the catalyst surface, allowing more electrons to effectively participate in the catalytic reaction. This enables the active centers of the catalyst to participate more fully in the reaction, enhancing catalytic activity.
[0072] Simultaneously, tests revealed that NiFe-S-6h-MOF / NF exhibited a higher conversion frequency (TOF, Figure 6(d)) and higher mass activity (MA, Figure 6(d)), indicating higher intrinsic catalytic activity. This demonstrates that the catalyst surface possesses the most electrocatalytic active sites and the highest intrinsic activity after sulfidation treatment. This implies that the catalyst can more effectively convert reactants, thereby enhancing its catalytic activity.
[0073] Simultaneously, the NiFe-S-6h-MOF / NF was found to have the highest double-layer capacitance (Cdl, in Figure 6(e), 4.09 mF cm⁻¹). -2This means that it has the highest electrochemical active surface area (ECSA). This indicates that after sulfidation treatment, NiFe-S-6h-MOF / NF, with its unique composite heterostructure of nanoparticles and flower-like nanosheet arrays, can provide more accessible active sites to improve OER catalytic activity, thus increasing the reaction rate and facilitating the adsorption and activation of reactants.
[0074] NiFe-S-6h-MOF / NF catalyst at 100 mA cm⁻¹ -2 A stability test was conducted at the current density for 200 hours. As shown in Figure 6(f), the catalytic activity did not show significant decline. This indicates that the NiFe-S-6h-MOF / NF catalyst prepared in Example 1 possesses excellent electrochemical stability and resistance to chloride ion corrosion. The stable catalyst can maintain its catalytic activity for a relatively long time and is not prone to deactivation. This is particularly crucial for catalytic reactions operating over extended periods, especially in industrial production.
[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A catalyst for the electrolysis of seawater, characterized in that, include: Nickel foam substrate material; An array of metal-organic framework nanosheets grown on the surface of the nickel foam substrate material, wherein the metal-organic framework contains nickel and iron; A sulfide layer deposited on the surface of the metal-organic framework nanosheet array, the sulfide layer comprising Ni3S4 nanoparticles.
2. The catalyst for seawater electrolysis as described in claim 1, characterized in that, The metal-organic framework is formed by the free assembly of the organic ligand NH2BDC with nickel and iron ions.
3. The catalyst for seawater electrolysis as described in claim 1, characterized in that, The metal-organic framework nanosheet array is flower-shaped, and the metal-organic framework nanosheet array and the Ni3S4 nanoparticles deposited on it form a composite heterostructure.
4. A method for preparing a catalyst for seawater electrolysis as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Using NH2BDC as an organic ligand, nickel and iron salts as metal salts, and nickel foam as a substrate material, a hydrothermal reaction was carried out in an alkaline environment to grow a metal-organic framework nanosheet array on the surface of nickel foam. Nickel foam with metal-organic framework nanosheet arrays grown on its surface was immersed in a sulfur source solution and subjected to a solvothermal reaction to obtain a catalyst for seawater electrolysis.
5. The preparation method according to claim 4, characterized in that, Before undergoing hydrothermal reaction, nickel foam undergoes pretreatment to remove surface oxides and impurities.
6. The preparation method according to claim 4, characterized in that, NH2BDC was dissolved in a mixed solution, nickel and iron salts were added, and the mixture was stirred until homogeneous. Then, an alkaline solution was added and mixed. The nickel foam was then introduced into the resulting solution for a hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature. The product was then rinsed and dried to obtain nickel foam with a metal-organic framework nanosheet array grown on its surface.
7. The preparation method according to claim 6, characterized in that, The mixed solution is obtained by mixing N,N-dimethylformamide, ethanol and water in a volume ratio of (14-18):1:1; Alternatively, the nickel salt may include nickel nitrate, nickel chloride, or nickel sulfate; Alternatively, the iron salt may include ferric nitrate, ferric chloride, or ferric sulfate; Alternatively, the molar ratio of NH2BDC, nickel salt, and iron salt is (1.2–1.3):(1–1.1):(0.2–0.3); the concentration of NH2BDC in the mixed solution is 0.03–0.04 mol / L. Alternatively, the concentration of the alkaline solution is 0.3–0.5 M, and the volume ratio of the alkaline solution to the mixed solution is (0.9–1.1):(17–19); Alternatively, the hydrothermal reaction is carried out at a temperature of 130–150°C for a time of 10–15 hours.
8. The preparation method according to claim 4, characterized in that, The sulfur source includes thioacetamide, thiourea, or sodium sulfide; The solvent of the sulfur source solution is an alcohol compound, preferably ethanol; the concentration of the sulfur source in the sulfur source solution is 0.2–0.3 mol / L. Alternatively, the solvothermal reaction is carried out at a temperature of 110–130°C for a reaction time of 1–12 h, preferably 1–11 h, and more preferably 6 h.
9. The application of a catalyst according to any one of claims 1-3 or a catalyst prepared by any one of claims 4-8 in the catalytic production of hydrogen from seawater.
10. A method for electrolyzing water, characterized in that, The catalyst used in the electrolysis process is the catalyst according to any one of claims 1-3 or the catalyst prepared by any one of claims 4-8; Preferably, the water is seawater.