Ce, Nd-MOF-5 / GO / PANI composite material, preparation method and application thereof

Abstract

The application discloses a Ce, Nd-MOF-5 / GO / PANI composite material, a preparation method and application thereof. A MOF-5 doped with double rare earth elements is modified as a skeleton, a three-dimensional conductive network is constructed by being combined with graphene oxide, and polyaniline with high conductivity is polymerized by using an in-situ polymerization method. The electrochemical behavior of the composite material is analyzed by performing a cyclic voltammetry test, and the significant advantages of the ternary composite structure in improving the electrode conductivity, promoting the reaction kinetics and enhancing the structural stability are verified, and the ternary composite structure is finally applied to a full vanadium redox flow battery.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology for vanadium redox flow batteries, specifically relating to a Ce, Nd-MOF-5 / GO / PANI composite material, its preparation method, and its application. The material uses MOF-5 modified with two rare earth elements (Ce, Nd) as a framework, constructs a three-dimensional conductive network by compositing it with graphene oxide (GO), and then polymerizes highly conductive polyaniline (PANI) using an in-situ polymerization method. Background Technology

[0002] Vanadium redox flow batteries, as a high-performance electrochemical energy storage technology, offer significant advantages such as independent power and capacity design, high safety, and long cycle life due to their electrolyte-based energy storage characteristic. They also boast rapid response, low cost, and reliability. Crucially, both the positive and negative electrode active materials are vanadium, eliminating the risk of cross-contamination between different active materials. As the core component of vanadium redox flow batteries, the material properties of the electrodes are key to improving the overall battery performance. This study aims to significantly improve the power density, coulombic efficiency, and rate performance of vanadium redox flow battery systems by modifying the electrode materials.

[0003] Metal-organic frameworks (MOFs) are porous crystalline materials constructed from metal ions / clusters and organic ligands through coordination bonds. They have attracted considerable attention due to their tunable pore size, high specific surface area, and diverse structures. However, their inherent low conductivity severely limits their direct application in electrode materials. To overcome this bottleneck, the introduction of rare earth elements has become an effective strategy. Rare earth elements, with their unique 4f electron configuration, large ionic radius, and strong electron transfer capabilities, can effectively modulate the electronic structure of MOFs, thereby improving their electrochemical performance. Furthermore, graphene oxide (GO), as a two-dimensional carbon material, possesses a high specific surface area, excellent mechanical strength, and abundant surface functional groups. Its two-dimensional structure can provide a large electrode / electrolyte interface, promoting transport and providing an ideal platform for composite modification. Polyaniline (PANI), due to its high conductivity, rapid and reversible redox reaction, and unique proton doping mechanism, shows great potential in the field of electrochemical energy storage.

[0004] Currently, research on the modification of vanadium redox flow battery (VRFB) electrode materials mainly focuses on single rare-earth-doped MOFs, while exploration of ternary composite systems constructed from dual rare-earth-doped MOFs and graphene oxide (GO) / polyaniline (PANI) remains relatively limited. Therefore, this study uses dual rare-earth-doped MOF-5 as the matrix material and composites it with GO and PANI to construct a ternary composite electrode with synergistic enhancement effects. By systematically exploring the electrochemical performance improvement mechanism and the synergistic effects between components, the study further evaluates the material's improvement effect on VRFB polarization effect, energy efficiency, and cycle stability. Summary of the Invention

[0005] To address the technical problems of insufficient conductivity, activity, and structural stability in existing electrode materials, this invention provides a method for preparing a dual rare-earth-doped MOF-5 / GO / PANI composite material via in-situ polymerization, along with its characterization and analysis, and investigates its electrochemical performance as an electrode material for vanadium redox flow batteries. This method employs ice-bath low-temperature in-situ polymerization technology to successfully synergistically combine Ce,Nd-MOF-5 with regular pores and rare-earth activity, graphene oxide (GO) with high specific surface area, and conductive polyaniline (PANI). Cyclic voltammetry analysis of the composite material reveals its significant advantages in improving electrode conductivity, promoting reaction kinetics, and enhancing structural stability. Finally, it is applied to vanadium redox flow batteries to investigate its improvement effects on battery coulombic efficiency, energy efficiency, and long-term cycle life.

[0006] The present invention aims to significantly improve the conductivity, electrochemical activity and reversibility of electrode materials through the above-mentioned multi-level composite synergistic process, thereby effectively solving the problems of low energy efficiency, coulombic efficiency decay, insufficient cycle stability and significant polarization effect of vanadium redox flow batteries at high current densities.

[0007] The first technical solution of this invention is: a method for preparing Ce,Nd-MOF-5 / GO / PANI composite material, wherein polymerization is carried out at low temperature in an ice bath, and the steps are as follows:

[0008] Ce,Nd-MOF-5 was synthesized using a hydrothermal method;

[0009] Graphene oxide sheets were prepared by using the modified Hummers method without adding NaNO3, with a mass ratio of potassium permanganate to graphite of 5-7:1.

[0010] Ce,Nd-MOF-5 / GO / PANI materials were prepared by precisely controlling the reaction process in an ice bath environment using in-situ polymerization.

[0011] The steps for preparing Ce,Nd-MOF-5 / GO / PANI material are as follows:

[0012] Graphene oxide sheets were dispersed in anhydrous ethanol and then subjected to ultrasonic treatment to form a uniform dispersion.

[0013] Ce,Nd-MOF-5 was dispersed in anhydrous ethanol to form a suspension, which was then poured into GO dispersion. The mixture was magnetically stirred under ice bath conditions to ensure thorough mixing and form a mixed suspension.

[0014] Add aniline monomer to the mixed suspension and continue stirring to allow aniline to penetrate into the Ce,Nd-MOF-5 channels;

[0015] Next, 0.1M HCl-ethanol solution was added and stirred to activate the aniline adsorbed on the Ce,Nd-MOF-5 surface and locally initiate polymerization;

[0016] Ammonium persulfate was dissolved in 1M HCl solution and slowly added dropwise to the above reaction system under continuous stirring, controlling the molar ratio of aniline to ammonium persulfate to be between 1:1 and 1:1.5;

[0017] The reaction system was stirred in an ice bath to complete the polymerization process. Finally, it was centrifuged to remove impurities. The resulting precipitate was washed with dilute hydrochloric acid until the supernatant was colorless and dried to finally obtain the Ce,Nd-MOF-5 / GO / PANI composite material.

[0018] Furthermore, the steps for synthesizing Ce,Nd-MOF-5 using the hydrothermal method are as follows:

[0019] First, weigh Zn(NO3)2·6H2O and H2BDC into a bottle, add DMF at room temperature, and stir until the solids are completely dissolved to form solution A;

[0020] Rare earth oxides were added to solution A according to a Zn: Ce: Nd molar ratio of 96:1-3:1-3, and stirring was continued until they were completely dissolved to form solution B.

[0021] Solution B was transferred to a reaction vessel, dried at a constant temperature, and subjected to a high-temperature and high-pressure reaction at 120°C before being cooled to room temperature.

[0022] The mixed solution was centrifuged, and the precipitate was washed with anhydrous ethanol until the supernatant became colorless. The resulting precipitate was then transferred and dried to obtain Ce,Nd-MOF-5.

[0023] Further, the steps for preparing graphene oxide sheets are as follows: under ice bath conditions, graphite powder is slowly added to a mixed acid with a volume ratio of 8:2 concentrated H2SO4 and H3PO4 and stirred to obtain a mixed solution. Then, potassium permanganate is slowly added to the above mixed solution and stirring is continued. After the ice bath is completed, the mixed solution is stirred and washed several times at a constant temperature until the supernatant is neutral. Then, the mixture is centrifuged and dried to obtain graphene oxide (GO) sheets.

[0024] The second technical solution of the present invention is as follows: The composite material obtained by the above preparation method uses Ce,Nd-MOF-5, GO materials and Ce,Nd-MOF-5 / GO / PANI as active materials, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder. The active material, conductive carbon black, and polyvinylidene fluoride are dispersed in N-methylpyrrolidone solvent at a mass ratio of 8:1:1. After grinding to form a uniform slurry, the slurry is uniformly loaded onto the surface of a carbon felt, controlling the active material loading on one side to be 2 mg / cm³. –2 The resulting composite electrode was then vacuum dried.

[0025] The third technical solution of the present invention is: the composite material obtained by the above preparation method is applied to an all-vanadium redox flow battery.

[0026] This invention determines the optimal molar ratio of Zn:Ce:Nd, a key component parameter for optimizing the electrochemical performance of materials. This ratio, while fully maintaining the stability of the MOF-5 main framework structure and the integrity of the conductive network, optimizes the performance of Ce³⁺. + With Nd³ + For Zn² + Co-doping at specific sites effectively modulates the electron distribution of the material and increases the number of electrochemically active sites. Different rare earth elements, due to their differences in outermost electron configurations, have significantly different effects on material performance after doping. If the doping ratio is too high, it will exacerbate lattice distortion and the formation of rare earth impurities, hindering charge transport kinetics, increasing interfacial impedance, and causing deactivation of active materials, ultimately leading to a sharp decline in rate performance and cycle stability. Conversely, if the doping ratio is too low, it is difficult to effectively introduce catalytic active centers and defect energy levels modulated by rare earth ions, resulting in a weak enhancement effect on electrode reaction kinetics. Therefore, this ratio plays a crucial role in achieving high conductivity, excellent electrocatalytic activity, and long-term cycle stability.

[0027] Beneficial effects

[0028] 1. The ice bath in-situ polymerization method of this invention not only effectively inhibits the excessively rapid polymerization of aniline monomers and avoids the aggregation of PANI, but also ensures that the crystal structure of Ce,Nd-MOF-5 and the lamellar structure of GO are not damaged, and finally achieves the synergistic compounding of the three in the same reaction system.

[0029] 2. Ce and Nd's unique 4f electron configuration can interact with Zn. 2+ The 3d orbitals of Ce exhibit energy level coupling, which effectively reduces the band gap of MOF-5 and introduces localized electronic states, significantly enhancing carrier concentration and forming an efficient charge transport path throughout the MOF framework. At the orbital interaction level, the 4f / 5d hybrid orbitals of Ce and the 4f orbitals of Nd exhibit good complementary properties. They synergistically hybridize with the O 2p orbitals in the structure, not only enhancing the covalent nature of the metal-oxygen bond and forming multiple bonds, but also significantly promoting charge delocalization and electronic transition efficiency, thereby improving the intrinsic conductivity and interfacial charge transfer capability of the material. Furthermore, Ce... 3+ / Ce 4+ With Nd 3+ / Nd 4+ Under electrochemical conditions, a reversible redox cycle can occur, which can act as a highly efficient electron donor / acceptor, providing power for continuous interfacial Faraday reactions and significantly enhancing the electrochemical activity and reaction kinetics of the material during charge and discharge. More importantly, rare earth ions, with their incompletely filled 4f orbitals, exhibit a unique affinity for vanadium ions (V), and can serve as highly efficient active sites to promote the adsorption and conversion of vanadium ions, thereby synergistically improving the overall performance of the all-vanadium redox flow battery.

[0030] 3. A highly efficient synergistic composite of Ce,Nd-MOF-5, graphene oxide (GO), and polyaniline (PANI) was successfully achieved under mild reaction conditions using an ice-bath in-situ polymerization method. This method not only effectively suppressed the excessively rapid polymerization of aniline monomers and prevented PANI aggregation by using low temperature, but also ensured the integrity of the Ce,Nd-MOF-5 crystal structure and the GO layered structure. The three components form a synergistic system with complementary functions. Ce,Nd-MOF-5 provides regular channels and rare-earth active sites, GO constructs a three-dimensional conductive network and inhibits MOF stacking, and PANI contributes pseudocapacitive properties to enhance charge storage and transport performance. Finally, a structurally stable and high-performance ternary composite material was successfully constructed in a single reaction system.

[0031] In summary, compared to GO and Ce,Nd-MOF-5 monomers, the Ce,Nd-MOF-5 / GO / PANI ternary composite material achieves significant structural and performance synergistic effects through sophisticated component design and an in-situ ice bath polymerization process. In this material, Ce,Nd-MOF-5 not only provides a regular pore structure and abundant rare-earth active sites, but its unique 4f electron configuration also interacts with Zn... 2+The 3D orbital coupling effectively reduces the material band gap and enhances charge transport capability; GO, as a two-dimensional conductive framework, constructs an efficient electron transport network while preventing MOF particle stacking, ensuring full utilization of the high specific surface area; PANI further enhances the charge storage and interfacial reaction kinetics of the composite material through its excellent pseudocapacitive properties. More importantly, Ce... 3+ / Ce 4+ With Nd 3+ / Nd 4+ The reversible redox cycle provides an additional electron transfer pathway for the system, synergistically enhancing the electrochemical activity of the material, while the special affinity of rare earth ions for vanadium species gives it a unique advantage in all-vanadium redox flow battery applications. Attached Figure Description

[0032] Figure 1 HOMO-LUMO bandgap diagram;

[0033] Figure 2 Ce,Nd-MOF-5 DOS diagram;

[0034] Figure 3 Scanning electron microscope images: a-Ce,Nd-MOF-5, b-GO, c-Ce,Nd-MO-5 / GO / PANI ternary composite materials;

[0035] Figure 4 X-ray diffraction pattern;

[0036] Figure 5 Infrared spectrum;

[0037] Figure 6 Cyclic voltammetry curve. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] Step 1: Preparation of Ce,Nd-MOF-5

[0041] First, 0.897 g of Zn(NO3)2·6H2O and 0.166 g of H2BDC were weighed into a 100 mL Erlenmeyer flask. 60 mL of DMF was added at room temperature, and the mixture was stirred with a magnetic stirrer for 15 min until the solids were completely dissolved to form solution A. Then, rare earth oxides were added to solution A at a Zn:Ce:Nd molar ratio of 96:2:2, and stirring continued for 30 min until completely dissolved to form solution B. Next, solution B was transferred to a Teflon-lined high-pressure reactor and placed in a constant-temperature drying oven. The reactor was subjected to high-temperature and high-pressure reaction at 120 °C for 24 h, followed by cooling to room temperature. Finally, the mixture was centrifuged at 8000 r / min for 10 min, repeated three times. The white precipitate was washed with anhydrous ethanol until the supernatant became colorless. The resulting precipitate was then transferred to an evaporating dish and dried overnight at 60 °C to obtain Ce,Nd-MOF-5 material.

[0042] Step 2: Preparation of graphene oxide

[0043] Under ice bath conditions, 60 mL of a mixed acid solution (8:2 volume ratio of concentrated H2SO4 to H3PO4) was added to a 500 mL beaker and stirred for two minutes to ensure uniform mixing. 2 g of graphite powder was weighed using an electronic balance and slowly added to the mixed acid solution, and stirred for 15 minutes to obtain a mixed solution. Then, 12.0 g of potassium permanganate was weighed using an electronic balance and slowly added to the mixed solution, and stirring was continued for 15 minutes. After the ice bath was completed, the mixed solution was transferred to a 45°C water bath and stirred at a constant temperature for 3 hours. After that, it was removed and placed at room temperature. 50 mL of pure water was slowly added in two portions while stirring. Hydrogen peroxide solution was then added dropwise until the solution turned bright yellow, indicating that GO had been successfully prepared.

[0044] Finally, wash the above mixed solution with deionized water until the supernatant is neutral, then discard the supernatant, dispense the mixture into centrifuge tubes and centrifuge at 4000 r / min for 10 min. Pour the precipitate into a beaker, add an appropriate amount of deionized water, and sonicate for about 2 h to make it a well mixed solution. Repeat the above centrifugation operation. After centrifugation, pour the precipitate into an evaporating dish and dry it in a 60 ℃ oven to obtain graphene oxide sheets.

[0045] Step 3: Preparation of Ce,Nd-MOF-5 / GO / PANI composite material

[0046] Ce,Nd-MOF-5 prepared in (1) and GO flakes prepared in (2) were dispersed in 20 mL of anhydrous ethanol and sonicated for 30 min to form a uniform dispersion. The Ce,Nd-MOF-5 suspension was then added to the GO dispersion and magnetically stirred for 30 min under ice bath conditions to ensure thorough mixing. 0.5 mL of aniline monomer was added to the mixed suspension, and stirring was continued for 1.5 h to allow aniline to preferentially penetrate the Ce,Nd-MOF-5 pores. Next, 0.5 mL of 0.1 M HCl-ethanol solution was added and stirred for 10 min to activate the aniline adsorbed on the Ce,Nd-MOF-5 surface and locally initiate polymerization. 1.56 g of ammonium persulfate was dissolved in 10 mL of 1 M HCl solution and slowly added dropwise to the above reaction system under continuous stirring, controlling the molar ratio of aniline to ammonium persulfate at 1:1.25. The reaction system was stirred in an ice bath for 12 h to complete the polymerization process. Finally, the mixed solution was centrifuged at 6000 r / min for 10 min, and this centrifugation and washing process was repeated three times to remove impurities. The resulting precipitate was washed with dilute hydrochloric acid until the supernatant was colorless, and then transferred to an evaporating dish and dried at 40 °C overnight to finally obtain the Ce,Nd-MOF-5 / GO / PANI composite material.

[0047] The molar ratio of aniline to ammonium persulfate is a key parameter determining the final oxidation state and electrochemical performance of polyaniline. Precise control of this ratio aims to synthesize polyaniline with an intrinsic state of emerald green imine base, in which the benzene ring and quinone ring alternate in an approximately 1:1 ratio, forming the structural basis for excellent conductivity. The quinone ring is the active site for proton acid doping, while the benzene ring constitutes an extended conjugated π-electron system. Their coexistence forms a unique "quinone ring-benzene ring-quinone ring" polaron structure. After doping, the quinone ring accepts protons and transforms into an imine structure, allowing electrons to efficiently delocalize along the conjugated backbone formed by the benzene ring, thus achieving high conductivity. If the oxidant ratio is too small (e.g., 1:0.75), oxidation is insufficient, and the product tends to be in a fully reduced state. Its chain segments are dominated by benzene rings, with a severe lack of quinone rings and effective doping sites, resulting in extremely poor conductivity. Conversely, if the oxidant ratio is too large (e.g., 1:1.5), over-oxidation occurs, and the product transforms into a fully oxidized state. Its chain segments are dominated by quinone rings, disrupting the alternating benzene-quinone ring conjugated structure, which also leads to loss of conductivity and material degradation. Therefore, a ratio of 1:1.25 precisely avoids both of these defects, ensuring the formation of the ideal intrinsic structure and laying the foundation for obtaining highly conductive and electrochemically active emerald green imine salts.

[0048] Example 2

[0049] The molar ratio of aniline to ammonium persulfate was 1:0.75. Other conditions were the same as in Example 1.

[0050] Example 3

[0051] The molar ratio of aniline to ammonium persulfate was 1:1. Other conditions were the same as in Example 1.

[0052] Example 4

[0053] The molar ratio of aniline to ammonium persulfate was 1:1.125. Other conditions were the same as in Example 1.

[0054] Example 5

[0055] The molar ratio of aniline to ammonium persulfate was 1:1.5. Other conditions were the same as in Example 1.

[0056] Example 6

[0057] The Zn:Ce:Nd molar ratio was 96:1:3. Other conditions were the same as in Example 1.

[0058] Example 7

[0059] The Zn:Ce:Nd molar ratio was 96:2:2. Other conditions were the same as in Example 1.

[0060] Example 8

[0061] The Zn:Ce:Nd molar ratio was 96:3:1. Other conditions were the same as in Example 1.

[0062] Figure 1 The image shows the HOMO-LUMO band gap of M1,M2-MOF-5. The energy difference between HOMO and LUMO (HOMO-LUMO band gap) is a key indicator of molecular stability and reactivity. A larger band gap implies higher electronic structure stability and lower excitation probability, often associated with chemical inertness and weak reactivity; while a smaller band gap indicates that the molecule is more prone to electronic transitions or recombination under external stimuli, with a lower excitation energy barrier, enhanced chemical activity and responsiveness, thus contributing to improved conductivity. Compared with undoped MOF-5 and single-doped MOF-5 in previous studies, the HOMO-LUMO band gap values ​​of the dual rare-earth co-doped systems (M1,M2-MOF-5) are generally lower, with band gap values ​​of 0.43, 0.35, and 0.47 eV for La,Nd-MOF-5, Ce,Nd-MOF-5, and Pr,Nd-MOF-5, respectively. This result confirms the positive effect of rare-earth co-doping on the conductivity of MOF-5. This phenomenon is attributed to the unique electronic structure of rare earth ions and the synergistic electronic effects between different rare earth ion pairs. Ce³ + 、Nd³ + 、Pr³ + Unfilled 4f orbitals of rare earth ions (and Ce³) + The 5d orbital can interact with Zn² in MOF-5.+ The orbitals of Ce³⁺ and LUMO cells couple and jointly regulate the electron distribution of the material, leading to a relative shift in the positions of the HOMO and LUMO energy levels, ultimately resulting in a decrease in the band gap. Taking Ce,Nd-MOF-5 as an example, its band gap (0.35 eV) is further reduced compared to single-doped Nd-MOF-5 (1.03 eV), mainly due to the coupling of Ce³⁺ and LUMO energy levels. + 4f / 5d orbitals with Nd³ + The 4f orbital in Zn² + Synergistic effects within the coordination environment. This synergistic effect not only introduces additional electronic states but also forms more efficient electron migration pathways, thereby significantly promoting electron transport and enhancing the overall conductivity of the material.

[0063] Figure 2 The diagram shows the DOS (Distribution of Optical Oscillation) of Ce,Nd-MOF-5. The unpaired 4f electrons of rare-earth ions result in a significantly higher DOS near the Fermi level for Ce,Nd-MOF-5 compared to previously studied undoped MOF-5 and monodoped M-MOF-5. (Dual rare-earth ion and Zn) 2+ The synergistic effect forms locally conductive clusters, reflected on the Zn 3d electron shoulders, synergistically enhancing the electronic conductivity of Ce,Nd-MOF-5 and increasing the overall electron density of the system. Throughout the energy range, Ce,Nd-MOF-5 exhibits significant spin polarization, with a clear asymmetry between its spin-up and spin-down channels, indicating that the dual rare-earth co-doping strategy can effectively induce magnetism and generate spin polarization. Furthermore, the energy level complementarity between the Ce 4f / 5d mixed orbitals and the Nd 4f orbitals hybridizes with the O 2p orbitals, forming multiple bonds that effectively promote charge delocalization and electron transitions. In summary, dual rare-earth doping, through multiple mechanisms including orbital hybridization, electronic structure modulation, and spin synergy, synergistically optimizes the electronic structure and charge transport behavior of MOF-5, successfully inducing spin polarization while significantly improving its conductivity.

[0064] Figure 3 Scanning electron microscope (SEM) images of three materials are shown. The microstructures of the three materials are clearly visible in the images. Figure 3 The Ce,Nd-MOF-5 shown in a still retains the typical cubic crystal structure of MOF-5; Figure 3 In this context, b represents GO, exhibiting its unique thin-layer folded morphology; Figure 3In the diagram, 'c' represents the electron microscopy structure of the Ce,Nd-MO-5 / GO / PANI ternary composite material. The cubic framework of Ce,Nd-MOF-5 remains clearly discernible, while its surface is encapsulated by PANI, forming a rough composite interface. This demonstrates the interweaving and interpenetration between the porous MOF framework and the polyaniline chains, introducing conductive pathways while preserving the porous structure. GO, as a two-dimensional supporting substrate, exhibits slight wrinkles on its surface, consistent with its monomer morphology. Its high specific surface area provides anchoring points for the upper materials and promotes electron transport and overall structural stability through physical contact. Furthermore, nanoscale polyaniline particles are uniformly dispersed on the GO surface or around the MOF composite mass, further enhancing the material's conductivity and active site density. This microstructure strongly confirms the successful composite formation of Ce,Nd-MOF-5, GO, and PANI components. Each component retains its characteristic morphology within the composite system while forming a synergistic ternary composite structure through interfacial interactions.

[0065] Figure 4 XRD patterns of GO, Ce,Nd-MOF-5, and Ce,Nd-MOF-5 / GO / PANI ternary composites are shown. As shown, GO exhibits a strong and sharp (001) characteristic diffraction peak at 2θ = 9.57°, attributed to the increased interlayer spacing caused by oxygen-containing functional groups on its surface, confirming that GO has a typical layered structure; the weak peak near 16° is also consistent with the structural characteristics of GO. For Ce,Nd-MOF-5, characteristic diffraction peaks consistent with the cubic MOF-5 structure are observed at 6.82° (200), 8.73° (220), 13.65° (400), 15.27° (024), and 19.36° (533), indicating that the material has been successfully synthesized and possesses a highly ordered three-dimensional channel structure. Among them, the (220) peak at 8.73° originates from the periodic arrangement of metal clusters along the diagonal direction, while the (400) crystal plane at 13.65° reflects the repeating units along the main crystal axis. In the XRD pattern of the ternary composite material, the (001) characteristic peak of GO at about 10° disappears significantly, indicating that the original layered stacking structure of GO is effectively dissociated during the composite process, successfully participates in the reaction and integrates into the composite system. At the same time, the originally clear diffraction peaks of Ce,Nd-MOF-5 after composite are significantly weakened or even disappear, indicating that its crystal structure is covered and isolated by the amorphous phase of PANI. Crystallinity is suppressed. PANI itself is amorphous or weakly crystalline, and its XRD usually shows broadened diffuse diffraction. The composite material as a whole exhibits amorphous diffuse characteristics dominated by PANI. Combined with the disappearance of the characteristic diffraction peaks of GO and Ce,Nd-MOF-5, it indicates that the three are not simply physically mixed, but rather form a structurally integrated composite material through interfacial interaction.

[0066] Figure 5 The FTIR spectra are for GO, Ce,Nd-MOF-5, and Ce,Nd-MOF-5 / GO / PANI ternary composites. In the GO spectrum, a position at 3180 cm⁻¹ is observed. –1 (Graphite carbon layer adsorbing –OH stretching vibration in water), 1718 cm –1 (C=O stretching vibration in carbonyl / carboxyl groups), 1622 cm –1 (Carbon ring C=C stretching vibration), 1365 cm –1 (–OH bending vibration), 1135 cm –1 (Stretching vibration of –OH in carboxylic acids), 1039 cm –1 (Epoxy group C–O stretching vibration) and 856 cm –1 Characteristic absorption peaks at locations such as (epoxy group out-of-plane bending vibrations) indicate that GO possesses a typical graphene oxide structure, and its abundant oxygen-containing functional groups provide reaction sites for subsequent composite formation. In the Ce,Nd-MOF-5 spectrum, at 1650 cm⁻¹... –1 With 1502 cm –1 The absorption peaks at 1600 cm⁻¹ are attributed to the asymmetric and symmetric stretching vibrations of the carboxyl group (–COOH) and the carbonyl group (C=O), respectively; –1 With 1395 cm –1 The peak at 10¹⁵ cm⁻¹ corresponds to the asymmetric and symmetric stretching vibrations of the C–O bonds coordinated with Zn; –1 The nearby small peak originates from the in-plane bending vibration of the C–H ring of terephthalic acid, 750 cm⁻¹ –1 With 826 cm –1 The small peak at 532 cm⁻¹ is attributed to the out-of-plane stretching vibration of the C–H group of the benzene ring. Furthermore, the peak at 532 cm⁻¹... –1 The absorption peak at 675 cm⁻¹ is characteristic of the stretching vibration of the Zn–O bond in the Zn₄O cluster. These results are consistent with previous reports, indicating that the MOF-5 structure has been successfully synthesized. Specifically, the absorption peak at 675 cm⁻¹ is characteristic of the stretching vibration of the Zn–O bond in the Zn₄O cluster. –1 The presence of rare-earth-oxygen bond (Ce–O / Nd–O) stretching vibration absorption peaks nearby confirms that Ce and Nd were successfully incorporated into the MOF-5 framework via coordination substitution. In the spectrum of the Ce,Nd-MOF-5 / GO / PANI ternary composite, although the characteristic peaks of GO and MOF-5 show some changes in intensity and shape (e.g., broadening of the O–H peak), the presence of their corresponding functional groups is still identifiable, indicating that GO participates in the composite and interacts with PANI and MOF-5 through hydrogen bonding or π–π stacking. Key peaks in MOF-5, such as C=O, the benzene ring framework, and metal-oxygen vibrations, are still preserved, indicating that its structure was not destroyed during the composite process. Furthermore, the composite exhibits a high absorption rate at 3658 cm⁻¹. –1 With 3270 cm –1The absorption peaks at 1615 cm⁻¹ are related to the N–H stretching vibrations of water molecules in PANI and the O–H stretching vibrations of GO / adsorbed water, respectively; –1 1476 cm –1 1136 cm –1 With 617 cm –1 The absorption peaks at these locations are attributed to C–C stretching of the quinone / benzene ring, N=Q=N (Q being the quinone ring) stretching, C–H vibration of the aromatic ring, and C–N imidazolide structure, respectively. The coexistence of all these characteristic functional groups further confirms the successful preparation of the Ce,Nd-MOF-5 / GO / PANI ternary composite material system.

[0067] Figure 6 The CV test results clearly demonstrate the differences in electrochemical performance among different materials. Due to its poor intrinsic conductivity, GO exhibits the lowest peak current and weak reversibility with significant polarization. In contrast, Ce,Nd-MOF-5 shows a significantly enhanced current response, indicating that rare-earth doping successfully introduces electrochemical activity. The Ce,Nd-MOF-5 / GO / PANI ternary composite material exhibits the best performance, with specific CV curve parameters shown in Table 1. Its peak current is increased by 3.4 × 10⁻⁶ compared to GO and Ce,Nd-MOF-5. –3 A and 1.21 × 10 –3 A. The activity order is: Ce,Nd-MOF-5 / GO / PANI > Ce,Nd-MOF-5 > GO. This order indicates that the increase in peak current corresponds to faster electrode reaction kinetics and more exposed active sites, reflecting the excellent charge transfer capability of the composite material at the electrode / electrolyte interface.

[0068] Table 1. CV parameters of Ce,Nd-MOF-5, GO, and Ce,Nd-MOF-5 / GO / PANI

[0069]

[0070] The significant performance improvement of the ternary composite material stems from the highly efficient synergistic system constructed by Ce,Nd-MOF-5, GO, and PANI. GO, as a conductive substrate, not only constructs a fast electron transport channel, but its high specific surface area and layered structure also provide ideal space for the uniform intercalation of Ce,Nd-MOF-5 particles and the adsorption of aniline monomers, effectively suppressing material aggregation. Ce,Nd-MOF-5, with its abundant porous structure and rare-earth metal centers, contributes a large number of redox active sites and provides an ideal site for aniline loading and polymerization. PANI, while imparting excellent conductivity to the system, introduces a significant pseudocapacitive effect, further enhancing interfacial reaction kinetics. The composite three-dimensional network formed by the synergy of these three components effectively suppresses the volume expansion of PANI during charge and discharge, while significantly promoting electron and ion transport efficiency and increasing the density of effective active sites, opening up a promising new avenue for the development of high-performance vanadium redox flow batteries and electrode materials.

Claims

1. A method for preparing a Ce,Nd-MOF-5 / GO / PANI composite material, characterized by, The polymerization is carried out under ice bath low temperature, and the steps are as follows: (1) Ce, Nd-MOF-5 is synthesized by using a hydrothermal method; (2) Graphene oxide sheets are prepared by using an improved Hummers method without adding NaNO3, and the mass ratio of oxidant potassium permanganate to graphite is 5-7:1; (3) Ce, Nd-MOF-5 / GO / PANI material is prepared by using an in-situ polymerization method to precisely control the reaction process under ice bath environment; The steps for preparing the Ce, Nd-MOF-5 / GO / PANI material are as follows: The graphene oxide sheets are dispersed in anhydrous ethanol, and a uniform dispersion liquid is formed by ultrasonic treatment; After the Ce, Nd-MOF-5 is dispersed in anhydrous ethanol to form a suspension, the suspension is poured into the GO dispersion liquid, and the two are fully mixed into a mixed suspension under magnetic stirring in an ice bath; Aniline monomer is added to the mixed suspension, and stirring is continued to allow the aniline to penetrate into the pores of the Ce, Nd-MOF-5; Then, 0.1M HCl-ethanol solution is added and stirred to activate the aniline adsorbed on the surface of the Ce, Nd-MOF-5 and locally initiate polymerization; Ammonium persulfate is dissolved in 1M HCl solution, and is slowly added to the above reaction system under continuous stirring, and the molar ratio of aniline to ammonium persulfate is controlled between 1:1 and 1:1.5; The reaction system is continuously stirred in an ice bath to complete the polymerization process, and finally, impurities are removed by centrifugation, the obtained precipitate is washed with dilute hydrochloric acid until the supernatant is colorless, dried, and finally the Ce, Nd-MOF-5 / GO / PANI composite material is obtained.

2. The production method according to claim 1, characterized by, The steps for synthesizing Ce, Nd-MOF-5 by using a hydrothermal method are as follows: First, Zn(NO3)2·6H2O and H2BDC are weighed in a bottle, DMF is added at room temperature, and stirring is continued until the solid is completely dissolved to form solution A; Rare earth oxides are added to solution A according to the molar ratio of Zn: Ce: Nd being 96:1-3:1-3, and stirring is continued until it is completely dissolved to form solution B; Solution B is transferred to a reaction kettle, and after high temperature and high pressure reaction, a mixed solution is obtained, which is cooled to room temperature; The mixed solution is centrifuged, the precipitate is washed with anhydrous ethanol until the supernatant becomes colorless, and then the obtained precipitate is transferred and dried to obtain doped Ce, Nd-MOF-5.

3. The preparation method according to claim 2, characterized in that, The molar ratio of Zn: Ce: Nd is 96:2:

2.

4. The preparation method according to claim 1, characterized in that, The steps for preparing graphene oxide sheets are as follows: graphite powder is slowly added to a mixed acid of concentrated H2SO4 and H3PO4 in a volume ratio of 8:2 under ice bath conditions to obtain a mixed solution, and then potassium permanganate is slowly added to the above mixed solution and continues to stir, after ice bath, constant temperature stirring is carried out for several times until the supernatant is neutral, then the mixture is centrifuged and dried to obtain graphene oxide GO sheets.

5. The preparation method according to claim 1, characterized in that, The molar ratio of aniline to ammonium persulfate is 1:

125.

6. The method of claim 1, wherein, The molar ratio of aniline to ammonium persulfate is 1:

1.

7. The preparation method according to claim 1, characterized in that, The molar ratio of aniline to ammonium persulfate is 1:1.

5.

8. The method of claim 1, wherein, The molar ratio of aniline to ammonium persulfate is 1:1.

25.

9. An electrode material, characterized by The composite material Ce,Nd-MOF-5 / GO / PANI obtained by the preparation method in any one of claims 1-8 is used as an active material, conductive carbon black is used as a conductive agent, and polyvinylidene fluoride is used as a binder, and the active material: conductive carbon black: polyvinylidene fluoride = 8:1:1 in mass ratio is dispersed in an N-methylpyrrolidone solvent, a uniform slurry is formed after grinding, and then the slurry is uniformly loaded on the surface of carbon felt, and the active material loading on one side is controlled to be 2 mg cm –2 , and the obtained electrode is vacuum dried.

10. The composite material obtained by the production process according to any one of claims 1-8 for use in a vanadium redox flow battery.

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