Oxygen Vacancy-Rich Mixed-Valence Cerium MOF: An Efficient Separator Coating to High-Performance Lithium-Sulfur Batteries

Metal Organic Frameworks as Polysulfide Reaction Modulators for Lithium Sulfur Batteries: Advances and Perspectives

Currently, lithium sulfur (Li-S) battery with high theoretical energy density has attracted great research interest. However, the diffusion and loss process of intermediate lithium polysulfide during charge-discharge hindered the application of the Li-S battery in modern life. To overcome this issue, metal organic frameworks (MOFs) and their composites have been regarded as effective additions to restrain the LiPS diffusion process for Li-S battery. Benefiting from the unique structure with rich active sites to adsorb LiPS and accelerate the LiPS redox, the Li-S batteries with MOFs modified exhibit superior electrochemical performance. Considering the rapid development of MOFs in Li-S battery, this review summarizes the recent studies of MOFs and their composites as the sulfur host materials, functional interlayer, separator coating layer, and separator/solid electrolyte for Li-S batteries in detail. In addition, the promising design strategies of functional MOF materials are proposed to improve the electrochemical performance of Li-S battery.

Pristine MOF Materials for Separator Application in Lithium-Sulfur Battery

Lithium-sulfur (Li-S) batteries have attracted significant attention in the realm of electronic energy storage and conversion owing to their remarkable theoretical energy density and cost-effectiveness. However, Li-S batteries continue to face significant challenges, primarily the severe polysulfides shuttle effect and sluggish sulfur redox kinetics, which are inherent obstacles to their practical application. Metal-organic frameworks (MOFs), known for their porous structure, high adsorption capacity, structural flexibility, and easy synthesis, have emerged as ideal materials for separator modification. Efficient polysulfides interception/conversion ability and rapid lithium-ion conduction enabled by MOFs modified layers are demonstrated in Li-S batteries. In this perspective, the objective is to present an overview of recent advancements in utilizing pristine MOF materials as modification layers for separators in Li-S batteries. The mechanisms behind the enhanced electrochemical performance resulting from each design strategy are explained. The viewpoints and crucial challenges requiring resolution are also concluded for pristine MOFs separator in Li-S batteries. Moreover, some promising materials and concepts based on MOFs are proposed to enhance electrochemical performance and investigate polysulfides adsorption/conversion mechanisms. These efforts are expected to contribute to the future advancement of MOFs in advanced Li-S batteries.

Versatile Separators Toward Advanced Lithium-Sulfur Batteries: Status, Recent Progress, Challenges and Perspective

Lithium-sulfur batteries (LSBs) have recently gained extensive attention due to their high energy density, low cost, and environmental friendliness. However, serious shuttle effect and uncontrolled growth of lithium dendrites restrict them from further commercial applications. As "the third electrode", functional separators are of equal significance as both anodes and cathodes in LSBs. The challenges mentioned above are effectively addressed with rational design and optimization in separators, thereby enhancing their reversible capacities and cycle stability. The review discusses the status/operation mechanism of functional separators, then primarily focuses on recent research progress in versatile separators with purposeful modifications for LSBs, and summarizes the methods and characteristics of separator modification, including heterojunction engineering, single atoms, quantum dots, and defect engineering. From the perspective of the anodes, distinct methods to inhibit the growth of lithium dendrites by modifying the separator are discussed. Modifying the separators with flame retardant materials or choosing a solid electrolyte is expected to improve the safety of LSBs. Besides, in-situ techniques and theoretical simulation calculations are proposed to advance LSBs. Finally, future challenges and prospects of separator modifications for next-generation LSBs are highlighted. We believe that the review will be enormously essential to the practical development of advanced LSBs.

Multifunctional Catalytic Hierarchical Interfaces of Ni12 P5 -Ni2 P Porous Nanosheets Enabled Both Sulfides Reaction Promotion and Li-Dendrite Suppression for High-Performance Li-S Full Batteries

The development of lithium-sulfur (Li-S) batteries is very promising and yet faces the issues of hindered polysulfides conversion and Li dendrite growth. Different from using different materials strategies to overcome these two types of problems, here multifunctional catalytic hierarchical interfaces of Ni12 P5 -Ni2 P porous nanosheets formed by Ni2 P partially in situ converted from Ni12 P5 are proposed. The unique electronic structure in the interface endows Ni12 P5 -Ni2 P effective electrocatalysis effect toward both sulfides' reduction and oxidation through reducing Gibbs free energies, indicating a bidirectional conversion acceleration. Importantly, Ni12 P5 -Ni2 P porous nanosheets with hierarchical interfaces also reduced the Li nucleation energy barrier, and a dendrite-free Li deposition is realized during the overall Li deposition and stripping steps. To this end, Ni12 P5 -Ni2 P decorated carbon nanotube/S cathode showing a high capacity of over 1500 mAh g-1 , and a high rate capability of 8 C. Moreover, the coin full cell delivered a high capacity of 1345 mAh g-1 at 0.2 C and the pouch full cell delivered a high capacity of 1114 mAh g-1 at 0.2 C with high electrochemical stability during 180° bending. This work inspires the exploration of hierarchical structures of 2D materials with catalytically active interfaces to improve the electrochemistry of Li-S full battery.

Dual-Ligand Strategy for the Design and Construction of a Cd-Zn Heterometallic Metal-Organic Framework by One-Pot Synthesis as a Heterogeneous Catalyst for the Epoxidation Reaction of Olefins

The use of metal-organic frameworks (MOFs) as catalysts is reported in various industrial applications. In contrast to monometallic MOFs, heterometallic MOFs with mixed organic ligands showed enhanced catalytic properties. The catalytic properties of heterometallic MOFs can be enhanced by generating defects and the synergistic effect between the two heterometals at secondary building units. By using a solvothermal technique, a Cd-Zn heterometallic MOF with a new morphology, [Cd2Zn(DPTTZ)0.5(OBA)3(H2O)(HCOOH)] (IUST-4) [DPTTZ = 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole, OBA = 4,4'-oxybis(benzoic acid)], was synthesized via a mixed-ligand strategy and characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. X-ray crystallographic analysis showed that IUST-4 is a neutral 3D metal-organic framework crystallized in the monoclinic system with space group C2/c. In this study, the catalytic properties of IUST-4 for the epoxidation of cyclooctene were investigated. IUST-4 was selected as the optimal catalyst for epoxy product production due to its high selectivity and yield. Moreover, the catalytic performance of IUST-4 was maintained despite five recycling cycles without significant degradation. The epoxidation of cyclooctene with IUST-4 has several advantages, including good selectivity, easy recovery, and short-time reaction.

Ce(IV)-Based Metal-Organic Gel for Ultrafast Removal of Trace Arsenate from Water

As a potential replacement for metal-organic frameworks (MOFs), constructing metal-organic gels (MOGs) is an appealing but challenging topic since MOGs are a kind of shapeable MOF gels. Also, the rapid adsorption of trace heavy metal ions in aqueous media remains a serious challenge. Herein, a simple strategy for the synthesis of Ce(IV)-based metal-organic gel (Ce-MOG) was first developed for the rapid adsorption of trace As(V). The (NH₄)₂Ce(NO₃)₆ obtains hydroxide bridges after adding apposite NaOH, leading to [Ce₆O₄(OH)₄]¹²⁺ clustering and inducing fast and excessive nucleation rates, which also leads to coordination disturbance of MOF nanocrystals to obtain Ce-MOG. The Ce-OH groups are the key to gel formation through hydrogen bonding and are the active site for the ultrafast adsorption of As(V). As expected, the resultant Ce-MOG has an excellent adsorption rate, making it possible to effectively decontaminate 500 ppb of As(V) to below the World Health Organization (WHO) recommended threshold for drinking water (10 ppb) within 1 min. It achieves equilibrium adsorption in 10 min, and the final arsenate-removing efficiency reaches 99.8%. For Ce-MOF, the effluent concentration of As(V) is higher than the drinking water standard, while equilibrium adsorption takes 60 min. The initial adsorption rate of Ce-MOG, h(k₂q_e²) is calculated and indicated to be 67.67 mg g^-1 min^-1, about 19.96 times that of Ce-MOF (3.39 mg g^-1 min^-1). As such, the excellent As(V) decontamination rate, selectivity, and reusability of Ce-MOG indicate its great potential for practical drinking water purification.

Recent Progress in Framework Materials for High-Performance Lithium-Sulfur Batteries

Lithium-Sulfur batteries (LSBs) have been considered as a promising candidate for the next generation of energy storage systems due to their high theoretical capacity. However, there are still lots of pending scientific and technological issues to be solved. Framework materials show great potential to address the above-mentioned issues due to the highly ordered distribution of pore sizes, effective catalytic activity, and periodically arranged aperture. In addition, good tunability gives framework materials unlimited possibilities to achieve satisfying performance for LSBs. In this review, the recent advances in pristine framework materials, their derivatives, and composites have been summarized. And a short conclusion and outlook regard to future prospects for guiding the development of framework materials and LSBs.

Ordered Mesoporous Carbon Grafted MXene Catalytic Heterostructure as Li-Ion Kinetic Pump toward High-Efficient Sulfur/Sulfide Conversions for Li-S Battery

Lithium-sulfur (Li-S) batteries exhibit unparalleled theoretical capacity and energy density than conventional lithium ion batteries, but they are hindered by the dissatisfactory "shuttle effect" and the sluggish conversion kinetics owing to the low lithium ion transport kinetics, resulting in rapid capacity fading. Herein, a catalytic two-dimensional heterostructure composite is prepared by evenly grafting mesoporous carbon on the MXene nanosheet (denoted as OMC-g-MXene), serving as interfacial kinetic accelerators in Li-S batteries. In this design, the grafted mesoporous carbon in the heterostructure can not only prevent the stack of MXene nanosheets with the enhanced mechanical property but also offer a facilitated pump for accelerating ion diffusion. Meanwhile, the exposed defect-rich OMC-g-MXene heterostructure inhibits the polysulfide shuttling with chemical interactions between OMC-g-MXene and polysulfides and thus simultaneously enhances the electrochemical conversion kinetics and efficiency, as fully investigated by in situ/ex situ characterizations. Consequently, the cells with OMC-g-MXene ion pumps achieve a high cycling capacity (966 mAh g-1 at 0.2 C after 200 cycles), a superior rate performance (537 mAh g-1 at 5 C), and an ultralow decaying rate of 0.047% per cycle after 800 cycles at 1 C. Even employed with a high sulfur loading of 7.08 mg cm-2 under lean electrolyte, an ultrahigh areal capacity of 4.5 mAh cm-2 is acquired, demonstrating a future practical application.

Flower-Shaped Hollow VOOH Spheres Wrapped by Carbon Nanotubes as the Cathode Electrocatalyst Enable Ultrafast and Long-Lasting Li-S Batteries

Lithium-sulfur batteries (LSBs) have been considered promising candidates for next-generation energy storage devices owing to their high energy density, low price, and environment-friendly characteristics. However, their commercialization has been hindered by the "shuttle effect", which occurs during the charge/discharge cycles and leads to poor cycling performance and low coulombic efficiency. Here, we synthesized flower-shaped hollow VOOH spheres on the carbon nanotube (CNT) network, which were used as the multifunctional sulfur host materials for the first time in LSBs. These VOOH spheres can chemically and physically confine polysulfides as well as catalyze their redox conversion; additionally, their hollow structure can effectively accommodate the volume change during cycling. Moreover, the CNTs among spheres can improve the conductivity of the host material and increase the number of active sites for interfacial reactions. Accordingly, when used as a cathode material, VOOH@CNTs/S composites exhibited a large specific discharge capacity of 1414.63 mAh/g at 0.1 C and excellent cycling stability. At a low current density of 0.5 C, VOOH@CNTs/S exhibited a capacity decay of 0.044% per cycle after 100 cycles. Importantly, at an ultrahigh current density of 5 C, a specific capacity as high as 455.09 mAh/g could be still be delivered after 1000 cycles, corresponding to a superior capacity retention of 90.46% and an ultralow capacity decay of 0.009% per cycle. These findings open up a new material for the practical application of LSBs with ultrafast charge/discharge property and long-lasting cyclic stability.

Thiol-Containing Metal-Organic Framework-Decorated Carbon Cloth as an Integrated Interlayer-Current Collector for Enhanced Li-S Batteries

Lithium-sulfur (Li-S) batteries hold great promise for new-generation energy storage technologies owing to their overwhelming energy density. However, the poor conductivity of active sulfur and the shuttle effect limit their widespread use. Herein, a carbon cloth decorated with thiol-containing UiO-66 nanoparticles (CC@UiO-66(SH)₂) was developed to substitute the traditional interlayer and current collector for Li-S batteries. One side of CC@UiO-66(SH)₂ acts as a current collector to load active materials, while the other side serves as an interlayer to further restrain polysulfide shuttling. This two-in-one integrated architecture endows the sulfur cathode with fast electron/ion transport and efficient chemical confinement of polysulfides. More importantly, rich thiol groups in the pores of UiO-66(SH)₂ serve to tether polysulfides by both covalent interactions and lithium bonding. Therefore, the Li-S battery equipped with this integrated interlayer-current collector not only delivers an enhanced specific capability (1209 mAh g^-1 at 0.1 C) but also exhibits prominent cycling stability (an attenuation rate of 0.037% per cycle for 1000 cycles at 1 C). Meanwhile, the battery achieves a high discharge capacity of 795 mAh g^-1 at a sulfur loading of 3.83 mg cm^-2. The new metal-organic framework (MOF)-based electrode material reported in this study undoubtedly provides insights into the exploration of functional MOFs for robust Li-S batteries.

Metal-Organic Frameworks Functionalized Separators for Lithium-Sulfur Batteries

Lithium sulfur batteries (LSBs) have attracted tremendous attention owing to their high theoretical specific capacity and specific energy. However, their practical applications are hindered by poor cyclic life, mainly caused by polysulfide shuttling. The development of advanced materials to mitigate the polysulfide shuttling effect is urgently demanded. Metal-organic frameworks (MOFs) have been exploited as multifunctional materials for the decoration of separators owing to their high surface area, structural diversity, tunable pore size, and easy tailor ability. In this review, we aim to present the state-of-the-art MOF-based separators for LSBs. Particular attention is paid to the rational design (pore aperture, metal node, functionality, and dimension) of MOFs with enhanced ability for anchoring polysulfides and facilitating Li⁺ transportation. Finally, the challenges and perspectives are provided regarding to the future design MOF-based separators for high-performance LSBs.

In Situ Fabrication of Porous Cox P Hierarchical Nanostructures on Carbon Fiber Cloth with Exceptional Performance for Sodium Storage

Superior high-rate performance and ultralong cycling life have been constantly pursued for rechargeable sodium-ion batteries (SIBs). In this work, a facile strategy is employed to successfully synthesize porous Co_x P hierarchical nanostructures supported on a flexible carbon fiber cloth (Co_x P@CFC), constructing a robust architecture of ordered nanoarrays. Via such a unique design, porous and bare structures can thoroughly expose the electroactive surfaces to the electrolyte, which is favorable for ultrafast sodium-ion storage. In addition, the CFC provides an interconnected 3D conductive network to ensure firm electrical connection of the electrode materials. Besides the inherent flexibility of the CFC, the integration of the hierarchical structures of Co_x P with the CFC, as well as the strong synergistic effect between them, effectively help to buffer the mechanical stress caused by repeated sodiation/desodiation, thereby guaranteeing the structural integrity of the overall electrode. Consequently, Co_x P@CFC as an anode shows a record-high capacity of 279 mAh g^-1 at 5.0 A g^-1 with almost no capacity attenuation after 9000 cycles.

Yb3+-Doped Two-Dimensional Upconverting Tb-MOF Nanosheets with Luminescence Sensing Properties

In this article, we synthesized a Yb³⁺-doped two-dimensional (2-D) upconverting Tb metal-organic framework (Tb-MOF) (hereinafter referred to as Tb-UCMOF) by a one-step solvothermal method. The synthesized Tb-UCMOF is composed of stacks of 2-D nanosheets with an average width distributed between 250 and 300 nm, and these nanosheets can be exfoliated by a simple liquid ultrasound method. The structural characteristics of this flaky particle accumulation are confirmed by the type IV adsorption-desorption isotherm with a H₃-type adsorption hysteresis loop, and the Brunauer-Emmett-Teller surface of Tb-UCMOF is 143.9257 m²·g^-1. Tb-UCMOF has characteristic emissions of Tb³⁺ which are located at 490, 545, 585, and 621 nm under 980 nm excitation. The upconverting luminescence mechanism is attributed to that Yb³⁺ absorbs multiple photons and transfers the energy to Tb³⁺, causing its 4f electrons to jump to the excited state, and then the upconverting emissions are obtained when electrons return to the ground state. Since the Tb-UCMOF nanosheets have high dispersibility and an obvious upconverting luminescent signal, we explored their luminescence sensing properties. The luminescence intensity is found to gradually decrease with the addition of Cu²⁺, the linear range of Cu²⁺ sensing is 0-1.4 μM, and the detection limit is 0.16 μM. This rapid, highly selective, and sensitive Cu²⁺ sensing indicates that 2-D upconverting MOF nanosheets have great application prospects in luminescence sensing and also promote the research of 2-D upconverting MOFs with specific recognition for the application of biological and environmental luminescent sensors.

A Novel Cerium(IV)-Based Metal-Organic Framework for CO2 Chemical Fixation and Photocatalytic Overall Water Splitting

Cerium (IV)-based metal-organic frameworks (MOFs) are highly desirable due to their unique potential in fields such as redox catalysis and photocatalysis. However, due to the high reduction potential of Ce^IV species in solution, it is still a great challenge to synthesize Ce^IV -MOFs with novel structures, which are extremely dominated by the hexanuclear Ce-O cluster inorganic building units (IBUs). Herein, a Ce-O IBU chain containing Ce^IV -MOF, CSUST-3 (CSUST: Changsha University of Science and Technology), was successfully prepared using the kinetic stabilization study of UiO-66(Ce)-NDC (H₂ NDC=2,6-naphthalenedicarboxylic acid). Furthermore, owing to the superior redox activity, Lewis acidity and semiconductor-like behavior owing to Ce⁴⁺ , activated CSUST-3 was demonstrated to be an excellent catalyst for CO₂ chemical fixation. One-pot synthesis of styrene carbonate from styrene and CO₂ was achieved under mild conditions (1 atm CO₂ , 80 °C, and solvent free). Moreover, activated CSUST-3 was shown to be a remarkable co-catalyst-free photocatalyst for overall water splitting (OWS), rendering 59 μmol g^-1  h^-1 of H₂ and 22 μmol g^-1  h^-1 of O₂ under simulated sunlight irradiation (Na₂ S-Na₂ SO₃ as sacrificial agent).

Highly catalytically active CoSe2 supported on nitrogen-doped three dimensional porous carbon as a cathode for high-stability lithium-sulfur battery

Lithium-sulfur batteries, promising secondary energy storage devices, were mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe 2 nanoparticles (CoSe 2 -PNC) is developed as a cathode for lithium-sulfur battery application. A combination of CoSe 2 and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6 mAh g -1 at a current density of 0.2 C. After 100 cycles, its capacity remained at 865.7 mAh g -1 corresponding to a capacity retention of 75.97%. In a long-term cycling test, a discharge specific capacity of 546.7 mAh g -1 was observed after 300 cycles performed at a current density of 1 C.

CoS2@montmorillonite as an efficient separator coating for high-performance lithium-sulfur batteries

The shuttle effect and sluggish redox kinetic of polysulfides still hinder the large-scale application of lithium-sulfur (Li-S) batteries. Herein, we adopt a CoS2-intercalated/coated-montmorillonite (CoS2@montmorillonite) composite to work as an efficient...

Progress and Prospect of Organic Electrocatalysts in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries featured by ultra-high energy density and cost-efficiency are considered the most promising candidate for the next-generation energy storage system. However, their pragmatic applications confront several non-negligible drawbacks that mainly originate from the reaction and transformation of sulfur intermediates. Grasping and catalyzing these sulfur species motivated the research topics in this field. In this regard, carbon dopants with metal/metal-free atoms together with transition-metal complex, as traditional lithium polysulfide (LiPS) propellers, exhibited significant electrochemical performance promotions. Nevertheless, only the surface atoms of these host-accelerators can possibly be used as active sites. In sharp contrast, organic materials with a tunable structure and composition can be dispersed as individual molecules on the surface of substrates that may be more efficient electrocatalysts. The well-defined molecular structures also contribute to elucidate the involved surface-binding mechanisms. Inspired by these perceptions, organic electrocatalysts have achieved a great progress in recent decades. This review focuses on the organic electrocatalysts used in each part of Li-S batteries and discusses the structure-activity relationship between the introduced organic molecules and LiPSs. Ultimately, the future developments and prospects of organic electrocatalysts in Li-S batteries are also discussed.

Multifunctional Ni–Mg bimetal-activated Zn(O,S) for hydrogen generation and environmental remediation with simulated solar-light irradiation

NMZ-S10 is a powerful and robust photocatalyst that is capable of conducting the hydrogen evolution reaction, chromium (Cr6+) reduction, mixed-dye degradation, and hydrogenation reaction under solar light illumination.