Multifunctional covalent organic framework with extended π-d conjugated structure for lithium–sulfur batteries

Abstract

Lithium–sulfur (Li–S) batteries hold great promise for the next generation of high energy density systems. However, sluggish sulfur conversion and the shuttle effect of polysulfides severely limit their commercial applications. Herein, a multifunctional covalent organic framework (Ni-COF) with extended π-d conjugated structure was synthesized and used for separator modification to overcome the obstacles in Li–S batteries. Ni-COF inherits the advantages of both COFs and conductive metal–organic frameworks, while compensating for their respective disadvantages. The abundant oxygen-containing groups in Ni-COF act as chemical adsorption sites to inhibit the shuttle effect of polysulfides. The designed π-d conjugated structure enhances electrical conductivity and provides high-density metal catalytic sites, thereby facilitating the conversion of polysulfides and enhancing the reaction kinetics of Li–S batteries. Consequently, the Li–S batteries with Ni-COF@PP separator exhibit remarkable rate performance of 719 mA h g⁻¹ at 4 C, along with a low attenuation rate of 0.087% per cycle over 300 cycles at 1 C. This study proposes a novel strategy for the rational design of COFs in Li–S batteries.

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Introduction

Lithium–sulfur batteries (Li–S batteries) hold significant promise as next-generation power supplies owing to their high energy density and low cost.^1–4 However, the practical application of Li–S batteries is still hindered by several factors, including the electronic insulation of sulfur and its discharge products (Li₂S₂ and Li₂S), the serious shuttle effect of soluble lithium polysulfides (LiPSs), large volume fluctuation, and lithium dendrites.^5–9 Separators, as a vital component of batteries, play a significant role in resolving the above critical issues. In recent years, the modification of conventional separators with functional materials has emerged as a pivotal area of research in the field of Li–S batteries.^10–13 Two-dimensional covalent organic frameworks (2D COFs), a class of crystalline porous polymers characterized by robust covalent bonds formed among organic building blocks, have emerged as functional materials in Li–S batteries due to their designable pore structures and tailored functionality.^14–18 Typically, 2D COFs designed for separators modification in Li–S batteries possess abundant chemical adsorption sites, such as –SO₃H groups, O and F atoms.^19–22 These groups can exhibit effective chemical adsorption of LiPSs, thereby suppressing the shuttle effects and enhancing the capacity and cycling stability of Li–S batteries.^23,24 However, despite the significant advances attained, further improvements are required for 2D COFs used in Li–S batteries. One significant challenge is the intrinsic poor electrical conductivity of COFs, which severely hinders electron transfer.^25,26 Additionally, the promotion of catalytic conversion of polysulfides to enhance the kinetics of Li–S batteries is crucial. However, the lack of metal catalytic sites in most COFs for electrocatalysis has also limited the advancement of COFs in Li–S batteries.

Another category of porous organic frameworks, 2D conductive metal–organic frameworks (2D cMOFs), formed by the coordinated bonds between organic ligands and metal nodes, have recently garnered attention due to their remarkable electron transport behavior.^27–30 Typically, 2D cMOFs are composed of orthosubstituted (NH₂, OH and SH) conjugated organic ligands and coordination linkages with metal ions. In comparison to 2D COFs, the high d (metal ions)-π (organic ligands) orbital overlap endows 2D cMOFs with extended π-d conjugation structure and strong electron delocalization through the whole skeleton, thereby showing high electron conductivity.^31–33 When employed to modify separators, the high conductivity of 2D cMOFs contributes to the rapid transfer of electrons, thus enhancing the reaction kinetics of LiPSs.^34,35 Additionally, the metal centers present in 2D cMOFs can be utilized as electrocatalytic active sites, thereby catalyzing the redox reaction of LiPSs. However, the composition of previously reported 2D cMOFs is primarily large organic ligands, resulting in a low density of metal ions. This leads to limited effectiveness in catalyzing the transformation of LiPSs. Moreover, the weak metal–ligand coordination bonds in 2D cMOFs, in comparison to the strong covalent bond linkages in 2D COFs skeletons, result in poor electrochemical and long-term stability. These limitations impede the practical feasibility of 2D cMOFs in energy storage applicaitons.^36,37 Given the aforementioned factors, the integration of the good chemical stability and abundant adsorption sites of 2D COFs with the beneficial conductivity and metal catalytic sites of 2D cMOFs into a porous framework holds considerable promise in yielding an optimal multifunctional material for separator modifications in Li–S batteries. However, the integration of the advantages of 2D COFs and 2D cMOFs remains a significant challenge, and the exploration of an ideal porous framework material for use in Li–S batteries is still in its infancy.

Herein, we address this challenge by developing a multifunctional 2D COF with an extended π-d conjugated structure, achieved by incorporating coordination sites at the corner regions of the COF skeleton. Since the high conductivity of 2D cMOFs is primarily attributed to their extended π-d conjugated structures, we propose introducing a similar conjugated system into the 2D COF framework to enhance electronic conductivity while retaining the intrinsic advantages of 2D COFs. As illustrated in Fig. 1, the coordinated metal ions in the COF designed in this work are positioned at the corner regions of the COF skeleton. This design significantly differs from traditional 2D cMOFs, where coordination sites typically serve as linkages within the overall framework, leading to poor chemical stability. Compared to previously reported porous materials, our design uniquely combines the adsorption sites and chemical stability of 2D COFs with the extended π-d conjugated structure of 2D cMOFs. Moreover, the smaller volume of π-conjugated organic ligands, coupled with the increased number of coordination sites within the COF, results in a higher density of metal ions than that of traditional 2D cMOFs.

Fig. 1 Schematic of the design strategy and synthesis of Ni-COF.

According to the aforementioned strategy, we constructed a multifunctional Ni-COF by coordinating Ni ions with two small-volume π-conjugated organic ligands through a simple one-step synthesis. The successful coordination of Ni ions into the N₂O₂ pocket within the corner regions of Ni-COF skeleton results in a higher metal density, significantly promoting the conversion of the LiPSs. Moreover, the strong hybridization between the d orbitals of Ni and the π orbitals of the organic ligands creates an extended π-d conjugation system in Ni-COF, thereby promoting the long-range electron delocalization and enhancing conductivity. Additionally, the abundant oxygen-containing groups within the Ni-COF backbones are preserved, serving as chemical adsorption sites for anchoring LiPSs. As a result, Ni-COF effectively combines the merits of 2D COFs and 2D cMOFs while mitigating their respective drawbacks, showing rich adsorption sites, numerous Ni catalytic sites, good electron conductivity, and excellent chemical stability. When used for separator modifications, Ni-COF effectively suppresses the shuttle effect of polysulfides and facilitates the lithium ions transport and catalytic conversion process. As a result, the Li–S batteries with Ni-COF@PP separator exhibited an outstanding rate performance of 719 mA h g⁻¹ at 4 C, and delivered a low attenuation rate of 0.087% per cycle over 300 cycles at 1 C. This work not only broadens the categories of COFs but also provides a new strategy for designing multifunctional COF-based separators for high-performance Li–S batteries.

Results and discussion

To achieve a higher metal density and construct a π-d conjugation system, two small-volume molecules, tetraminobenzoquinone (TABQ) and 2,5- hydroxyterephthalaldehyde (HBC), were selected as organic ligands. As shown in Fig. 1, the nitrogen atom from TABQ and the hydroxyl oxygen atom from HBC collectively create N₂O₂ pockets. The Ni atoms coordinate within the inner N₂O₂ pockets, forming Ni-N₂O₂ units in the corner regions of the COF covalent skeleton. Additionally, the Ni-N₂O₂ units are further bridged by the benzene ring of HBC, yielding an extended π-d conjugation system. In this regard, a multifunctional COF (denoted as Ni-COF) was synthesized by reacting HBA and TABQ with Ni(OAc)₂·4H₂O via a simple one-step synthesis (Fig. 1, see details in ESI†).

The chemical structure of Ni-COF was analyzed by Fourier-transform infrared (FT-IR). As shown in Fig. 2a, the appearance of a characteristic C=N stretching vibration at 1540 cm⁻¹, along with the absence of –NH₂ and the –CHO stretching modes from the initial monomers, indicate the formation of C=N linkage in Ni-COF.³⁸ In addition, the peak at 1652 cm⁻¹ in Ni-COF corresponds to the C=O bands, attributed to the quinone carbonyl groups in TABQ, further confirming the successful preparation of Ni-COF. The permanent porous structure of Ni-COF was assessed by the nitrogen sorption isotherm at 77 K. The specific surface area value of Ni-COF is 51.45 m² g⁻¹. The low specific surface area of Ni-COF might be caused by the disordered stacking of COF layers due to the interlayer repulsion between the polarized C=O/C=N functional groups.^39–41 Besides, the partial occupation of the COF channels by Ni ions also leads to a reduction in the specific surface area.^42–45 As shown in Fig. 2b, Ni-COF displays type-I uptakes behavior, indicating its microporous properties. The pore size distribution determined by the nonlocal density functional theory (NLDFT) method exhibits a peak centered at 1.09 nm. This value closely matches the theoretical pore size of Ni-COF (1.10 nm), confirming the successful construction of the designed framework structure shown in Fig. 1.

Fig. 2 (a) FT-IR spectra of HBC, TABQ and Ni-COF. (b) N₂ adsorption–desorption curves and pore size distribution profile of Ni-COF (inset image). (c) Experimental and simulated PXRD patterns of Ni-COF. (d) Top and side view of the AA stacking model of Ni-COF. (e–g) HRTM images of Ni-COF.

The crystalline nature of Ni-COF was identified by powder X-ray diffraction (PXRD). As displayed in Fig. 2c, three intense diffraction peaks at 2θ = 7.0°, 8.5° and 11.5° are observed, which can be assigned to the (110), (020) and (200) plane, respectively, indicating the high crystallinity of Ni-COF. Pawley refinement was further conducted using the experimental PXRD data. As shown in Fig. 2d, Ni-COF is arranged in an AA stacking mode, with unit cell parameters of a = 15.4129 Å, b = 20.6895 Å, c = 3.5606 Å, and α = β = γ = 90°. The refined XRD profile closely matches with the PXRD pattern, as evidenced by the good agreement factors (R_p = 3.34%, R_wp = 5.80%). Moreover, as shown in Fig. 2e–g, the high-resolution Transmission electron microscopy (HRTEM) images of Ni-COF show a clear long-range ordered arrangement structure, further revealing its excellent crystallinity. Additionally, the chemical stability of Ni-COF was also demonstrated by the nearly unchanged PXRD patterns of samples immersed in various organic solvents for three days (Fig. S1†). This result conforms that incorporating Ni-N₂O₂ units into the corners of Ni-COF does not compromise the integrity of the main covalent backbone, which remains robustly held together by strong covalent bonds. The excellent chemical stability, especially in electrolyte solvents, highlights the promising potential of Ni-COF for use in Li–S batteries.

The chemical composition of Ni-COF was analyzed by X-ray photoelectron spectroscopy (XPS) measurement. As shown in Fig. S2,† the XPS spectra confirm the existence of C, N, O and Ni elements, along with the formation of the C=N linkages. Notably, the high-resolution Ni 2p spectrum (Fig. 3a) shows the Ni 2p_3/2 and Ni 2p_1/2 peaks at 856.2 and 874.2 eV, respectively, indicating a Ni oxidation state of +2 in Ni-COF.⁴⁶ Furthermore, the Ni contents in Ni-COF was determined to be 25.72 wt% by inductively coupled plasma atomic emission spectroscopy (ICP), closely aligning with the theoretical content of 22.72 wt% (Table S1†). The scanning electron microscopy (SEM) images and elemental mapping of Ni-COF (Fig. S3†) display its microrod-like morphologies and the homogeneous distribution of Ni elements in Ni-COF. This high density and well-distributed Ni ions in Ni-COF is expected to result in outstanding catalytic performance for Li–S batteries.

Fig. 3 (a) High resolution Ni 2p XPS spectra of Ni-COF. (b) Ni K-edge XANES spectra of Ni-COF, NiO and Ni foil. (c) Ni K-edge EXAFS spectra of Ni-COF, NiO and Ni foil. (d) Wavelet transform (WT) of Ni K-edge EXAFS data for Ni foil, (e) NiO and (f) Ni-COF. (g) Electrostatic potential distributions of Ni-COF. (h) PDOS of Ni-COF.

Furthermore, the X-ray absorption near edge structure (XANES) spectra of the Ni K-edge in Ni-foil, NiO and Ni-COF were collected to analyze the valence state of Ni and its coordination structure in Ni-COF. In Fig. 3b, the absorption edge for Ni-COF is closer to that of NiO than metallic Ni, illustrating that the Ni elements in Ni-COF existed in +2 valence state, consistent with the XPS results. Additionally, the extended X-ray absorption fine structure (EXAFS) spectrum of Ni-COF shows a characteristic peak at 1.5 Å, corresponding to Ni–O(N) coordinating bonds (Fig. 3c). Wavelet transform (WT) analysis were further conducted on the Ni K-edge EXAFS data of Ni-COF, NiO and Ni foil. The horizontal axis represents the wave vector number k, which is crucial for distinguishing different types of coordination atoms.⁴⁷ As shown in Fig. 3d–f, the main intensity maximum at ∼5.2 Å⁻¹ in the pattern of Ni-COF is almost identical to the position of NiO and clearly different from that of Ni foil, providing further evidence of the Ni–O(N) coordinated structure. These results confirm that the Ni-N₂O₂ units are successfully constructed in Ni-COF via one-step synthesis method. With its unique conjugation structure and chemical composition, Ni-COF is expected to be an ideal multifunctional material for separator modification in Li–S batteries.

Furthermore, density functional theory (DFT) computations were employed to analyze the electrostatic potential distribution of Ni-COF. As shown in Fig. 3g, the O atoms in the framework of Ni-COF causes obvious negative charge accumulation (red color region) inside the channel, which can form the nucleophilic interaction toward LiPSs. That is to say, the Ni-COF can block polysulfides via both electrostatic repulsion (i.e., repelling polysulfide anions) and chemical trapping (i.e., adsorbing molecular LiPSs).^19,21 The projected density of states (PDOS) of Ni-COF (Fig. 3h) show distinct overlap between the Ni d orbitals of Ni and the p orbitals of N/O atoms, illustrating the high electron coupling and strong coordination interaction of Ni–N/O bonds.⁴⁸ Furthermore, the solid-state UV-vis absorption spectrum of Ni-COF (Fig. S5†) shows a strong broad absorption bands in the region 350 nm to 660 nm, which is attributed to the Ligand-To-Metal-Charge-Transition (LMCT) π–π* excitations of the extended π-conjugated system.^49,50 This result indicates the strong electron delocalization between the organic ligands and metal orbitals in Ni-COF, further confirming the successful construction of metal–ligand π-d conjugation. As anticipated, this extended π-d conjugated structure endows Ni-COF with a good electron conductivity of 9.1 × 1.0⁻⁴ S m⁻¹ measured by four-probe method. The extended π-d conjugation system and enhanced conductivity of Ni-COF are expected to promote the fast electron transfer in Li–S batteries.

The as-synthesized Ni-COF was uniformly coated on the surface of the PP separator to serve as a modified layer and enhance the electrochemical performance of Li–S batteries. As shown in Fig. S6,† after coating with Ni-COF, the macropores of the pristine PP separator are fully covered by Ni-COF with a thickness of ∼15 μm. As displayed in Fig. 4a, the contact angle (CA) between the Ni-COF@PP separator and the electrolyte is 13.3°, which is significantly smaller than that of the PP separator (32.0°). This finding indicates that the Ni-COF modified layer effectively improves the wettability of Ni-COF@PP separator towards the electrolyte, thereby promoting the ions transport.

Fig. 4 (a) Contact angle test of PP separator and (b) Ni-COF modified separator. (c) I–t curves of Li/Li symmetric cells with different PP and (d) Ni-COF@PP, inset is EIS plots of the symmetric cell. (e) EIS plots of PP and Ni-COF, and locally enlarged EIS plots of PP and Ni-COF. (f) Li⁺ conductivities and Li⁺ transference numbers of PP and Ni-COF.

To further evaluate the ions transport behavior of different separators, the ionic conductivity and Li⁺ transference number were evaluated, respectively. Based on the experimental results (Fig. 4c and d), Ni-COF@PP demonstrates a higher Li⁺ transference number (0.76) compared to the PP separator (0.32), indicating enhanced cations (Li⁺) transport and suppression anions migration. This result suggests that Ni-COF as separator modified layer greatly facilitate the lithium ions transport. Additionally, the ionic conductivity of Ni-COF@PP separator is calculated to be 1.70 mS cm⁻¹, significantly higher than that of PP separator (0.49 mS cm⁻¹) (Fig. 4e and f). The electrostatic potential result of Ni-COF (Fig. 2g) reveals that the improved Li⁺ transference number of Ni-COF@PP can be attributed to the negatively charged oxygen atoms in Ni-COF, which efficiently hinders anions transport while promoting cations migration.^19,21 The good wettability and enhanced Li⁺ selective transport of Ni-COF@PP are greatly beneficial for improving the rate performance of Li–S batteries.

The adsorption of Ni-COF on LiPSs was subsequently investigated by visible LiPSs adsorption experiments and UV-vis spectroscopy. As shown in Fig. 5a, the immersion of Ni-COF in a Li₂S₆ solution results in a clear fading of the Li₂S₆ solution's color, thereby suggesting its effective adsorption capabilities towards LiPSs. The UV-vis spectra demonstrates that the strong absorbance bands of Li₂S₆ at ∼280 nm weaken considerably after the addition of Ni-COF, further confirming the strong adsorption capability of Ni-COF.⁵¹ To verify the electrocatalytic properties of Ni-COF towards the liquid–liquid conversion of LiPSs, CV tests were conducted using Li₂S₆–Li₂S₆ symmetric cells in the voltage range of −1.0 to 1.0 V. As shown in Fig. 5b, the CV curve of the symmetric cell with Ni-COF shows distinct redox peaks with higher redox current and lower voltage polarization compared to the cells with bare PP, indicating accelerated redox kinetics.^20,33 It can be attributed to the higher electrical conductivity of Ni-COF and the catalytic activity contributed by the abundant Ni metal catalytic sites in Ni-COF. Additionally, the liquid–solid conversion of LiPSs was further investigated through Li₂S nucleation and growth experiments. The potentiostatic discharge curves of Li₂S precipitation at 2.05 V based on different materials are presented in Fig. 5c and d. The deposition capacity is also calculated based on the mass of sulfur in the electrolyte. The results clearly show that Li₂S nucleation occurs earlier in the cell with Ni-COF@SP compared to the PP-based cell, suggesting faster kinetics for the liquid–solid conversion. Furthermore, the deposition capacity of Li₂S for Ni-COF-based (191.0 mA h g⁻¹) significantly exceeds that of PP-based (110.3 mA h g⁻¹), even within a shorter nucleation and growth time, further demonstrating the high catalytic activity of Ni-COF for Li₂S deposition. The rapid Li₂S nucleation and efficient catalytic effect during LiPSs conversion can be largely attributed to the excellent catalytic properties of the high-density Ni sites in Ni-COF.

Fig. 5 (a) Visible LiPSs adsorption experiments and UV-vis spectroscopy of Ni-COF. Inset: photograph of pristine Li₂S₆ and Li₂S₆ solution after being absorbed by Ni-COF. (b) CV curves of the Li₂S₆ symmetric cell. (c and d) Potentiostatic discharge tests of Li₂S₈/tetraglyme solution with different electrodes at 2.05 V. (e) CV profiles of Li–S batteries with PP and Ni-COF@PP separator at 0.1 mV s⁻¹. (f) The Tafel plots derived from CV curves calculated from the reduction peaks. (g) Rate performance of Li–S batteries based on different separators. (h) Galvanostatic discharge–charge profiles at various current density of Li–S batteries with PP and (i) Ni-COF@PP separators. (j) Cycling performance of Li–S batteries at 1C over 300 cycles with PP and Ni-COF@PP separators.

The electrochemical performance of Li–S batteries with different separators was evaluated by paring lithium anode with sulfur cathode. CV measurements were conducted to study the redox behaviors of the batteries. As shown in Fig. 5e, the redox peak currents of the batteries with Ni-COF@PP separator are significantly higher than those of the batteries with PP separator, indicating that the batteries with Ni-COF@PP have a higher capacity. For quantitative analysis, Tafel plots of the redox peaks were analyzed to illustrate the sulfur redox reaction kinetics. As presented in Fig. 5f, the Tafel slopes for the cell with Ni-COF@PP separator (72.1 mV dec⁻¹) is lower than that of PP separator (80.7 mV dec⁻¹), which indicates the enhanced reduction kinetics in Li–S batteries.³³ In addition, the Tafel curves (Fig. S7†) according to the oxidative peaks also verify that the Ni ions in Ni-COF can considerably accelerate the oxidation kinetics for the reaction of Li₂S/Li₂S₂ → S, further demonstrating the high catalytic activity of Ni-COF.

Additionally, to further confirm the fast reaction kinetics, the CV measurements of the Li–S batteries assembled with different separators at various scanning rates were performed (Fig. S8†). Then, the Li⁺ diffusion coefficient (D_Li+) was analyzed by the CV curves on different scan rates and calculated by the Randles–Sevcik equation.²⁰ As shown in Fig. S9,† the corresponding D_Li+ of peak R₁ and peak R₂ of the Ni-COF@PP-based batteries are calculated to be ∼10⁻⁸ cm² s⁻¹ and 10⁻⁷ cm² s⁻¹, respectively, which are much higher than those of the PP separator. The corresponding D_Li+ for the two oxidation peaks of the Ni-COF@PP-based batteries are also higher than those of the PP separator, further indicating the faster lithium-ions diffusion behaviors for the former batteries. The rate performance of Li–S batteries with different separators were evaluated at various current densities. As displayed in Fig. 5g, the Li–S batteries with PP separator deliver capacities of 681, 553, 482, and 458 mA h g⁻¹ at 0.5, 1.0, 2.0, and 4.0 C, respectively. In contrast, the Li–S batteries with Ni-COF@PP separator display superior rate capabilities, achieving 964, 852, 778, and 719 mA h g⁻¹ at 0.5, 1.0, 2.0, and 4.0 C, respectively. The remarkable rate capacities can be attributed not only to the fast ion transport ability of Ni-COF, but also to the increased electronic conductivity of Ni-COF. The enhanced electronic transfer ability promotes the charge transfer during the redox process, thus synergistically enhancing the performance of Li–S batteries.^51–54 Furthermore, the capacity-voltage profiles in Fig. 5h, i and S10 show that Ni-COF@PP-based batteries exhibit not only a higher specific capacity but also a smaller voltage polarization compared to PP-based batteries, demonstrating the effectiveness of Ni-COF modified layer in enhancing sulfur utilization and accelerating polysulfide conversion kinetics. The cycle stability of batteries with different separators were evaluated. As shown in Fig. S11,† the battery with a Ni-COF@PP separator delivers a high initial capacity of 880 mA h g⁻¹, outperforming that of PP separator (679 mA h g⁻¹). The reversible specific capacity of the battery using a Ni-COF modified separator is 688 mA h g⁻¹ after 200 cycles. While the Li–S battery with the PP separator displays a capacity of 506 mA h g⁻¹ after 200 cycles. Moreover, as shown in Fig. 5j, the Li–S battery with the PP separator displays an initial capacity of 598 mA h g⁻¹ and a capacity of 374 mA h g⁻¹ after 300 cycles under a current density of 1C. While the Li–S battery with the Ni-COF@PP separator delivers a higher initial capacity of 827 mA h g⁻¹ and a reversible capacity of 609 mA h g⁻¹ after 300 cycles with a capacity retention rate of 74%, higher than that using the PP separator (63%). The capacity increase during the initial cycle is mainly attributed to the better electrolyte infiltration and improved Li⁺ diffusion kinetics during cycling.^55,56 The above results fully demonstrate that Ni-COF as a multifunctional separator modification material effectively promotes the reaction kinetics of Li–S batteries and improves the capacity, long-cycle stability and rate performance.

Conclusions

In summary, we synthesized a multifunctional Ni-COF with an extended π-d conjugated structure and used it to modify the separator of Li–S batteries, proposing a strategy to solve the issues of polysulfide shuttle and sluggish redox kinetics. Compared with the previous reports, Ni-COF successfully integrated the merits of 2D COFs and 2D cMOFs while mitigating their respective drawbacks, possessing rich adsorption sites, numerous Ni catalytic sites, excellent electron conductivity, and good chemical stability. When used for separator modification, Ni-COF effectively suppressed the shuttle effect of polysulfides and facilitated the lithium ions transport and catalytic conversion process, which greatly enhanced the cycling stability and rate capability of Li–S batteries. This study demonstrates that constructing π-d conjugated structures in COFs is an effective strategy to improve the overall electrochemical performance of Li–S batteries.

Data availability

The original data supporting this article are available in the main text and ESI.†

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (22209155 and 52201283) and China Postdoctoral Science Foundation (2024M752941, 2022TQ0291, and 2022M712869), and Henan Postdoctoral Science Foundation (HN2024059) and Frontier Exploration Projects of Longmen Laboratory (LMQYTSKT021).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5qi00119f

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