Self-Assembly of 0D-2D Heterostructure Electrocatalyst from MOF and MXene for Boosted Lithium Polysulfide Conversion Reaction

Defect-rich porous graphitic phase carbon nitride layer grafted MXene as desolvation promoter for efficient sulfur conversion in extremely harsh conditions

Lithium-sulfur (Li-S) batteries exhibit superior theoretical capacity and energy density but are still hindered by the sluggish redox conversion kinetic of lithium polysulfides arising from the significant desolvation barrier, especially under high current density or low-temperature environments. Herein, a two-dimensional (2D) porous graphitic phase carbon nitride/MXene (CN-MX) heterostructure with intrinsic defects was designed via electrostatic adherence and in-situ thermal polycondensation. In the design, the defect-rich CN with abundant catalytic activity and porous structure could efficiently facilitate the lithium polysulfides capture, the dissociation of solvated lithium-ion (Li+), and fast Li+ diffusion. Concurrently, 2D MXene nanosheets with high electronic conductivity could act as charge transport channels and provide electrochemical active sites for sulfur redox reactions. The Li-S cells with CN-MX heterostructure modified separator demonstrated uncommon rate performance (945 mAh/g at 4.0 C) and satisfactory areal capacity (5.5 mAh cm-2 at 0.2 C). Most remarkably, even at 0 °C, the assembled Li-S batteries performed favorable cycle stability (91.6% capacity retention after 100 cycles at 0.5 C) and outstanding rate performance (695 mAh/g at 2.0 C), and superior high loading performance (5.1 mAh cm-2 at 0.1 C). This work offers exciting new insights to enable Li-S batteries to operate in extreme environments.

Unveiling the scope and perspectives of MOF-derived materials for cutting-edge applications

Although synthesis and design of MOFs are crucial factors to the successful implementation of targeted applications, there is still lack of knowledge among researchers about the synthesis of MOFs and their derived composites for practical applications. For example, many researchers manipulate study results, and it has become quite difficult to quit this habit specifically among the young researchers Undoubtedly, MOFs have become an excellent class of compounds but there are many challenges associated with their improvement to attain diverse applications. It has been noted that MOF-derived materials have gained considerable interest owing to their unique chemical properties. These compounds have exhibited excellent potential in various sectors such as energy, catalysis, sensing and environmental applications. It is worth mentioning that most of the researchers rely on commercially available MOFs for use as precursor supports, but it is an unethical and wrong practice because it prevents the exploration of the hidden diversity of similar materials. The reported studies have significant gaps and flaws, they do not have enough details about the exact parameters used for the synthesis of MOFs and their derived materials. For example, many young researchers claim that MOF-based materials cannot be synthesized as per the reported instructions for large-scale implementation. In this regard, current article provides a comprehensive review of the most recent advancements in the design of MOF-derived materials. The methodologies and applications have been evaluated together with their advantages and drawbacks. Additionally, this review suggests important precautions and solutions to overcome the drawbacks associated with their preparation. Applications of MOF-derived materials in the fields of energy, catalysis, sensing and environment have been discussed. No doubt, these materials have become excellent class but there are still many challenges ahead to specify it for the targeted applications.

N-Vacancy Enriched Porous BN Fibers for Enhanced Polysulfides Adsorption and Conversion in High-Performance Lithium-Sulfur Batteries

Severe shuttle effect of soluble polysulfides and sluggish redox kinetics have been thought of as the critical issues hindering the extensive applications of lithium-sulfur batteries (LSBs). Herein, one-dimensional boron nitride (1D BN) fibers with abundant pores and sufficient N-vacancy defects were synthesized using a thermal crystallization following a pre-condensation step. The 1D structure of BN facilitates unblocked ions diffusion pathways during charge/discharge cycles. The embedded pores within the polar BN strengthen the immobilization of polysulfides via both physical confinement and chemical interaction. Moreover, the highly exposed active surface area and intentionally created N-vacancy sites substantially promote reaction kinetics by lowering the energy barriers of the rate-limiting steps. After incorporating with conductive carbon networks and elemental S, the as-prepared S/Nv-BN@CBC cathode of LSBs deliver an initial discharge capacity of up to 1347 mAh g-1 at 200 mA g-1, while maintaining a low decay rate of 0.03 % per cycle over 1000 cycles at 1600 mA g-1. This work offers an effective strategy to mitigate the shuttle effect and highlights the significant potential of defect-engineered BN in accelerating the reaction kinetics of LSBs.

Advances and challenges in MXene-based electrocatalysts: unlocking the potential for sustainable energy conversion

MXenes, a novel class of two-dimensional materials, have garnered significant attention for their promising electrocatalytic properties in various energy conversion applications such as water splitting, fuel cells, metal-air batteries, and nitrogen reduction reactions. Their excellent electrical conductivity, high specific surface area, and versatile surface chemistry enable exceptional catalytic performance. This review highlights recent advancements in the design and application strategies of MXenes as electrocatalysts, focusing on key reactions including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and nitrogen reduction reaction (NRR). We discuss the tunability of MXenes' layered structures and surface properties through surface modification, MXene lattice substitution, defect and morphology engineering, and heterostructure construction. Despite the considerable progress, MXenes face challenges such as restacking during catalysis, stability issues, and difficulties in large-scale production. Addressing these challenges through innovative engineering approaches and advancing industrial synthesis techniques is crucial for the broader application of MXene-based materials. Our review underscores the potential of MXenes in transforming electrocatalytic processes and highlights future research directions to optimize their catalytic efficiency and stability.

0D-2D multifunctional bimetallic MOF derivative-MXene heterojunction for high areal capacity lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have attracted much attention due to their high specific capacity. However, at high loads and rates, the polysulfides conversion rate and ion transport of batteries are slow, limiting their commercialization. This work reports zero-dimensional (0D) bimetallic MOF derivatives grown in situ on two-dimensional (2D) MXene by electrostatic adsorption (FeCo@Ti3C2). The 0D bimetallic structure effectively avoids the stacking of MXene while providing a dual catalytic site for polysulfides. The 2D structure of MXene also provides a large number of pathways for the rapid diffusion of lithium ions. This 0D-2D heterostructured heterogeneous catalyst with bimetallic synergistic active sites efficiently immobilizes and catalyzes polysulfides, providing a fast charge transfer pathway for the electrochemical reaction of lithium polysulfides. The Li-S battery with this multifunctional 0D-2D heterojunction structure catalyst has outstanding high rate capacity (703 mAh g-1 at 4 C at room temperature and 555 mAh g-1 at 2 C at 0 °C), fascinating capacity at high load (5.5 mAh cm-2 after 100 cycles at a high sulfur content of 8.2 mg cm-2). The study provides new ideas for the commercialization of high-efficiency Li-S batteries.

In Situ Construction of Bimetallic Selenides Heterogeneous Interface on Oxidation-Stable Ti3C2Tx MXene Toward Lithium Storage with Ultrafast Charge Transfer Kinetics

Ti3C2Tx (MXene) is widely acknowledged as an excellent substrate for constructing heterogeneous structures with transition metal chalcogenides (TMCs) for boosting the electrochemical performance of lithium-ion storage. However, conventional synthesis strategies inevitably lead to poor electrochemical charge transfer due to Ti3C2Tx-derived TiO2 at the heterogeneous interface between Ti3C2Tx and TMCs. Here, an innovative in situ selenization strategy is proposed to replace the originally generated TiO2 on Ti3C2Tx with metallic TiSe2 interphase, clearing the bottleneck of slow charge transfer barrier caused by MXene oxidation. The construction of bimetallic selenide formed by CoSe2 and TiSe2 generates intrinsic electric fields to guide the fast ion diffusion kinetics in a heterogeneous interface. Additionally, the CoSe2/TiSe2/Ti3C2Tx heterogeneous structure with enhanced structural stability and improved rate performance is confirmed by both experiments and theoretical calculations. The engineered heterogeneous structure exhibits an ultra-high pseudocapacitance contribution (73.1% at 0.1 mV s-1), rendering it well-suited to offset the kinetics differences between double-layer materials. The assembled lithium-ion capacitor based on CoSe2/TiSe2/Ti3C2Tx possesses a high energy density and an ultralong life span (89.5% after 10 000 times at 2 A g-1). This devised strategy provides a feasible solution for utilizing the performance advantages of MXene substrates in lithium storage with ultrafast charge transfer kinetics.

Enhancing Lithium-Sulfur Battery Performance with MXene: Specialized Structures and Innovative Designs

Established in 1962, lithium-sulfur (Li-S) batteries boast a longer history than commonly utilized lithium-ion batteries counterparts such as LiCoO2 (LCO) and LiFePO4 (LFP) series, yet they have been slow to achieve commercialization. This delay, significantly impacting loading capacity and cycle life, stems from the long-criticized low conductivity of the cathode and its byproducts, alongside challenges related to the shuttle effect, and volume expansion. Strategies to improve the electrochemical performance of Li-S batteries involve improving the conductivity of the sulfur cathode, employing an adamantane framework as the sulfur host, and incorporating catalysts to promote the transformation of lithium polysulfides (LiPSs). 2D MXene and its derived materials can achieve almost all of the above functions due to their numerous active sites, external groups, and ease of synthesis and modification. This review comprehensively summarizes the functionalization advantages of MXene-based materials in Li-S batteries, including high-speed ionic conduction, structural diversity, shuttle effect inhibition, dendrite suppression, and catalytic activity from fundamental principles to practical applications. The classification of usage methods is also discussed. Finally, leveraging the research progress of MXene, the potential and prospects for its novel application in the Li-S field are proposed.

2D Se-Rich ZnSe/CoSe2@C Heterostructured Composite as Ultrastable Anodes for Alkaline-Ion Batteries

2D transitional metal selenide heterostructures are promising electrode materials for potassium-ion batteries (PIBs) owing to the large surface area, high mechanical strength, and short diffusion pathways. However, the cycling performance remains a significant challenge, particularly concerning the electrochemical conversion reaction. Herein, 2D Se-rich ZnSe/CoSe2@C heterostructured composite is fabricated via a convenient hydrothermal approach followed by selenization process, and then applied as high-performance anodes for PIBs. For example, the capacity delivered by the heterostructured composite is mainly contributed to the synergistic effect of conversion and alloy/de-alloy processes aroused by K+, where K+ may highly insert or de-insert into Se-rich ZnSe/CoSe2@C. The obtained electrode delivers an outstanding reversible charge capacity of 214 mA h g-1 at 1 A g-1 after 4000 cycles for PIBs, and achieves 262 mAh g-1 when coupled with a PTCDA cathode in the full cell. The electrochemical conversion mechanism of the optimized electrode during cycling is investigated through in situ XRD, Raman, and ex situ HRTEM. In addition, the heterostructured composite as anodes also displays excellent electrochemical performances for sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs). This work opens up a new window for investigating novel electrode materials with excellent capacity and long durability.

Efficient Hydrogen Generation from Ammonia Borane Hydrolysis on a Tandem Ruthenium-Platinum-Titanium Catalyst

Hydrolysis of ammonia borane (NH3BH3, AB) involves multiple undefined steps and complex adsorption and activation, so single or dual sites are not enough to rapidly achieve the multi-step catalytic processes. Designing multi-site catalysts is necessary to enhance the catalytic performance of AB hydrolysis reactions but revealing the matching reaction mechanisms of AB hydrolysis is a great challenge. In this work, we propose to construct RuPt-Ti multi-site catalysts to clarify the multi-site tandem activation mechanism of AB hydrolysis. Experimental and theoretical studies reveal that the multi-site tandem mode can respectively promote the activation of NH3BH3 and H2O molecules on the Ru and Pt sites as well as facilitate the fast transfer of *H and the desorption of H2 on Ti sites at the same time. RuPt-Ti multi-site catalysts exhibit the highest turnover frequency (TOF) of 1293 min-1 for AB hydrolysis reaction, outperforming the single-site Ru, dual-site RuPt and Ru-Ti catalysts. This study proposes a multi-site tandem concept for accelerating the dehydrogenation of hydrogen storage material, aiming to contribute to the development of cleaner, low-carbon, and high-performance hydrogen production systems.

One-step growth of ultrathin CoSe2 nanobelts on N-doped MXene nanosheets for dendrite-inhibited and kinetic-accelerated lithium-sulfur chemistry

The practical application of lithium-sulfur (Li-S) batteries is inhibited by the shuttle effect of lithium polysulfides (LiPSs) and slow polysulfide redox kinetics on the S cathode as well as the uncontrollable growth of dendrites on the Li metal anode. Therefore, both cathode and anode sides must be considered when modifying Li-S batteries. Herein, two-dimensional (2D) ultrathin CoSe2 nanobelts are in situ grown on 2D N-doped MXene nanosheets (CoSe2@N-MXene) via one-step solvothermal process for the first time. Owing to its unique 2D/2D structure, CoSe2@N-MXene can be processed to crumpled nanosheets by freeze-drying and flexible and freestanding films by vacuum filtration. These crumpled CoSe2@N-MXene nanosheets with abundant active sites and inner spaces can act as S hosts to accelerate polysulfide redox kinetics and suppress the shuttle effect of LiPSs owing to their strong adsorption ability and catalytic conversion effect with LiPSs. Meanwhile, the CoSe2@N-MXene film (CoSe2@NMF) can act as a current collector to promote uniform Li deposition because it contains lithiophilic CoSe2 and N sites. Under the systematic effect of CoSe2@N-MXene on S cathode and Li metal anode, the electrochemical and safety performance of Li-S batteries are improved. CoSe2@NMF also shows excellent storage performances in flexible energy storage devices.

Constructing Orbital Coupling-Modulated Homogeneous Dual-Atom Fe-Fe Sites for Boosting Bidirectional Conversion of Polysulfides

Homogeneous dual-atom catalysts (HDACs) have garnered significant attention for their potential to overcome the shuttling effect and sluggish reaction kinetics in lithium-sulfur (Li-S) batteries. However, modulating the electron structure of metal atomic orbitals for HDACs to dictate the catalytic activity toward polysulfides has remained meaningful but unexplored so far. Herein, an interfacial cladding strategy is developed to obtain a new type of dual-atom iron matrix with a unique FeN2P1-FeN2P1 coordination structure (Fe2@NCP). The 3d orbital electrons of the Fe centers are redistributed by incorporating phosphorus atoms into the first coordination sphere. The theoretical calculations disclose that the strong coupling between the Fe d orbital and the S p orbital exhibits an enhanced Fe-S bond and improved reactivity toward polysulfides. Moreover, the Fe2@NCP catalyst achieves robust adsorption ability toward Li2Sn (1 ≤ n ≤ 8) and significantly boosts bidirectional sulfur redox reaction kinetics by lowering the Li2S deposition/decomposition energy barriers. Consequently, the assembled Li-S batteries present a high retention ratio of 77.3% after 500 cycles at 1C. Furthermore, the Li-S pouch cell also exhibits good performance at 0.1C (80.2% retention over 100 cycles) for practical application with a sulfur loading of 4.0 mg/cm2. The outcome of this study will facilitate the design of homogeneous dual-atom catalysts for Li-S batteries.

Se-p Orbitals Induced "Strong d-d Orbitals Interaction" Enable High Reversibility of Se-Rich ZnSe/MnSe@C Electrode as Excellent Host for Sodium-Ion Storage

The heterostructure of transition-metal chalcogenides is a promising approach to boost alkali ion storage due to fast charge kinetics and reduction of activation energy. However, cycling performance is a paramount challenge that is suffering from poor reversibility. Herein, it is reported that Se-rich particles can chemically interact with local hexagonal ZnSe/MnSe@C heterostructure environment, leading to effective ions insertion/extraction, enabling high reversibility. Enlightened by theoretical understanding, Se-rich particles endow high intrinsic conductivities in term of low energy barriers (1.32 eV) compared with those without Se-rich particles (1.50 eV) toward the sodiation process. Moreover, p orbitals of Se-rich particles may actively participate and further increase the electronegativity that pushes the Mn d orbitals (dxy and dx2-y2) and donate their electrons to dxz and dyz orbitals, manifesting strong d-d orbitals interaction between ZnSe and MnSe. Such fundamental interaction will adopt a well-stable conducive electronic bridge, eventually, charges are easily transferred from ZnSe to MnSe in the heterostructure during sodiation/desodiation. Therefore, the optimized Se-rich ZnSe/MnSe@C electrode delivered high capacity of 576 mAh g-1 at 0.1 A g-1 after 100 cycles and 384 mAh g-1 at 1 A g-1 after 2500 cycles, respectively. In situ and ex situ measurements further indicate the integrity and reversibility of the electrode materials upon charging/discharging.

Advances in Aqueous Zinc Ion Batteries based on Conversion Mechanism: Challenges, Strategies, and Prospects

Recently, aqueous zinc-ion batteries with conversion mechanisms have received wide attention in energy storage systems on account of excellent specific capacity, high power density, and energy density. Unfortunately, some characteristics of cathode material, zinc anode, and electrolyte still limit the development of aqueous zinc-ion batteries possessing conversion mechanism. Consequently, this paper provides a detailed summary of the development for numerous aqueous zinc-based batteries: zinc-sulfur (Zn-S) batteries, zinc-selenium (Zn-Se) batteries, zinc-tellurium (Zn-Te) batteries, zinc-iodine (Zn-I2) batteries, and zinc-bromine (Zn-Br2) batteries. Meanwhile, the reaction conversion mechanism of zinc-based batteries with conversion mechanism and the research progress in the investigation of composite cathode, zinc anode materials, and selection of electrolytes are systematically introduced. Finally, this review comprehensively describes the prospects and outlook of aqueous zinc-ion batteries with conversion mechanism, aiming to promote the rapid development of aqueous zinc-based batteries.

Nanofiber-Reinforced MXene/rGO Composite Aerogel for a High-Performance Piezoresistive Sensor and an All-Solid-State Supercapacitor Electrode Material

The assembly of two-dimensional (2D) nanomaterials into a three-dimensional (3D) aerogel can effectively prevent the problem of restacking. Here, nanofiber-reinforced MXene/reduced graphene oxide (rGO) conductive aerogel is prepared via the hydrothermal reduction of GO using pyrrole and in situ composite with MXene. Combined with low-content 2D conductive nanosheets (MXene and rGO) as "brick", conductive polypyrrole as "mortar", and one-dimensional (1D) nanofiber as "rebar", a strong interfacial cross-linking of MXene and rGO nanosheets is realized through covalent and noncovalent bonds to synergistically improve its mechanical performance. Based on the prepared MXene/rGO aerogel, a high-performance piezoresistive sensor with a sensitivity of up to 20.80 kPa-1 in a wide pressure range of 15.6 kPa is obtained, and it can withstand more than 5000 cyclic compressions. Besides, the sensor shows a stable output and can be applied to monitor various human motion signals. In addition, an all-solid-state supercapacitor electrode is also fabricated, which shows a high area-specific capacitance of up to 274 mF/cm2 at a current density of 1 mA/cm2.

Triple Effect of "Conductivity-Adsorption-Catalysis" Enables MXene@FeCoNiP to be Sulfur Hosts for Lithium-Sulfur Batteries

The weak chemical immobilization ability and poor catalytic effect of MXene inhibit its application in lithium-sulfur (Li-S) batteries. Herein, a novel MXene@FeCoNiP composite is rationally developed and utilized as a sulfur host for Li-S batteries. In this well-designed MXene-based nanostructure, the introduction of FeCoNiP in the interlayer of MXene nanosheets can not only effectively inhibit the restacking of MXene nanosheets but also act as an accelerator for the adsorption and catalysis of polysulfides to restrain the shuttling effect and facilitate the transformation of polysulfides. The existence of two-dimensional MXene nanosheets provides more active sites and improves the conductivity, which is beneficial for accelerating the reaction kinetics. Thus, the as-prepared MXene@FeCoNiP composites achieve an outstanding performance for Li-S batteries. This work provides an opportunity to construct an ideal sulfur host with the triple effect of "conductivity-adsorption-catalysis".

Advanced Insights on MXenes: Categories, Properties, Synthesis, and Applications in Alkali Metal Ion Batteries

The development and optimization of promising anode material for next-generation alkali metal ion batteries are significant for clean energy evolution. 2D MXenes have drawn extensive attention in electrochemical energy storage applications, due to their multiple advantages including excellent conductivity, robust mechanical properties, hydrophilicity of its functional terminations, and outstanding electrochemical storage capability. In this review, the categories, properties, and synthesis methods of MXenes are first outlined. Furthermore, the latest research and progress of MXenes and their composites in alkali metal ion storage are also summarized comprehensively. A special emphasis is placed on MXenes and their hybrids, ranging from material design and fabrication to fundamental understanding of the alkali ion storage mechanisms to battery performance optimization strategies. Lastly, the challenges and personal perspectives of the future research of MXenes and their composites for energy storage are presented.

Heterogenization-Activated Zinc Telluride via Rectifying Interfacial Contact to Afford Synergistic Confinement-Adsorption-Catalysis for High-Performance Lithium-Sulfur Batteries

The notorious shuttle effect and sluggish conversion kinetics of intermediate polysulfides (Li2S4, Li2S6, Li2S8) are severely hindered the large-scale development of Lithium-sulfur (Li-S) batteries. Rectifying interface effect has been a solution to regulate the electron distribution of catalysts via interfacial charge exchange. Herein, a ZnTe-ZnO heterojunction encapsulated in nitrogen-doped hierarchical porous carbon (ZnTe-O@NC) derived from metal-organic framework is fabricated. Theoretical calculations and experiments prove that the built-in electric field constructed at ZnTe-ZnO heterojunction via the rectifying interface contact, thus promoting the charge transfer as well as enhancing adsorption and conversion kinetics toward polysulfides, thereby stimulating the catalytic activity of the ZnTe. Meanwhile, the nitrogen-doped hierarchical porous carbon acts as confinement substrate also enables fast electrons/ions transport, combining with ZnTe-ZnO heterojunction realize a synergistic confinement-adsorption-catalysis toward polysulfides. As a result, the Li-S batteries with S/ZnTe-O@NC electrodes exhibit an impressive rate capability (639.7 mAh g-1 at 3 C) and cycling performance (70% capacity retention at 1 C over 500 cycles). Even with a high sulfur loading, it still delivers a superior electrochemical performance. This work provides a novel perspective on designing highly catalytic materials to achieve synergistic confinement-adsorption-catalysis for high-performance Li-S batteries.

Juice Vesicles Bioreactors Technology for Constructing Advanced Carbon-Based Energy Storage

The construction of high-quality carbon-based energy materials through biotechnology has always been an eager goal of the scientific community. Herein, juice vesicles bioreactors (JVBs) bio-technology based on hesperidium (e.g., pomelo, waxberry, oranges) is first reported for preparation of carbon-based composites with controllable components, adjustable morphologies, and sizes. JVBs serve as miniature reaction vessels that enable sophisticated confined chemical reactions to take place, ultimately resulting in the formations of complex carbon composites. The newly developed approach is highly versatile and can be compatible with a wide range of materials including metals, alloys, and metal compounds. The growth and self-assembly mechanisms of carbon composites via JVBs are explained. For illustration, NiCo alloy nanoparticles are successfully in situ implanted into pomelo vesicles crosslinked carbon (PCC) by JVBs, and their applications as sulfur/carbon cathodes for lithium-sulfur batteries are explored. The well-designed PCC/NiCo-S electrode exhibits superior high-rate properties and enhanced long-term stability. Synergistic reinforcement mechanisms on transportation of ions/electrons of interface reactions and catalytic conversion of lithium polysulfides arising from metal alloy and carbon architecture are proposed with the aid of DFT calculations. The research provides a novel biosynthetic route to rational design and fabrication of carbon composites for advanced energy storage.

Rapid Growth of Bi2Se3 Nanodots on MXene Nanosheets at Room Temperature for Promoting Sulfur Redox Kinetics

Li-S batteries are hampered by problems with their cathodes and anodes simultaneously. The improvement of Li-S batteries needs to consider both the anode and cathode. Herein, a Bi2Se3@MXene composite is prepared for the first time by rapidly growing Bi2Se3 nanodots on two-dimensional (2D) MXene nanosheets at room temperature through simply adding high-reactive hydroxyethylthioselenide in Bi3+/MXene aqueous solution. Bi2Se3@MXene exhibits a 2D structure due to the template effect of 2D MXene. Bi2Se3@MXene can not only facilitate the conversion of lithium polysulfides (LiPSs) but also inhibit their shuttling in the S cathode due to its catalytic effect and adsorption force with LiPSs. Bi2Se3@MXene can also be used as an interfacial lithiophilic layer to inhibit Li dendrite growth in the Li metal anode. Theoretical calculations reveal that Bi2Se3 nanodots in Bi2Se3@MXene can effectively boost the adsorption ability with LiPSs, and the MXene in Bi2Se3@MXene can accelerate the electron transport. Under the bidirectional regulation of Bi2Se3@MXene in the Li metal anode and S cathode, the Li-S battery shows an enhanced electrochemical performance.

A precisely Assembled Wall-Like Architecture for High Lithium/Sodium Storage

MXene nanosheets and ordered porous carbons both have their own advantages and disadvantages. Assembling and combining the advantages of the two will be a good choice for battery electrode hosts of active materials. In this work, an electrostatic separation-adsorption strategy is proposed to realize the ordered alternating self-assembly of MXene nanosheets and ordered porous carbon (MPOC), obtaining a unique wall-like porous material with a high conductivity and interconnected porous nanostructure, which strengthens the transfer rate of electrons and ions simultaneously. Meanwhile, the introduction of N-doping from porous carbon into MPOC prolongs the cycle life. When use red phosphorus (RP) as active materials, the MPOC@RP anode exhibited high-capacity output (2454.3 and 2408.1 mAh g-1 in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) at 0.1 C) and long cycle life (the decay rates per cycle of 0.028% and 0.036% after 1500 and 1200 cycles at 2 C in LIBs and SIBs respectively). The successful application in RP anodes displays great potential in other electrode materials such as silicon, sulfur, selenium, and so on. Meanwhile, this strategy is also effective to design other composites materials like MXene and carbon nanotubes, MXene and Graphene, and so on.

Ultrathin nitrogen-doped carbon Ti3C2Tx-TiN heterostructure derived from ZIF-8 nanoparticles sandwiched MXene for high-performance capacitive deionization

Rational design of high-performance electrode materials is crucial for enhancing desalination performance of capacitive deionization (CDI). Here, ultrathin nitrogen-doped carbon/Ti3C2Tx-TiN (NC/MX-TiN) heterostructure was developed by pyrolyzing zeolite imidazolate framework-8 (ZIF-8) nanoparticles sandwiched MXene (ZSM), which were formed by assembling ultrafine ZIF-8 nanoparticles with size of 20 nm on both sides of MXene nanosheets. The introduction of ultrasmall ZIF-8 particles allowed for in situ nitridation of the MXene during pyrolysis, forming consecutive TiN layers tightly connected to the internal MXene. The two-dimensional (2D) heterostructure exhibited remarkable properties, including high specific surface area and excellent conductivity. Additionally, the resulting TiN demonstrated exceptional redox capability, which significantly enhanced the performance of CDI and ensured cycling stability. Benefiting from these advantages, the NC/MX-TiN exhibited a maximum adsorption capacity of 45.6 mg g-1 and a steady cycling performance in oxygenated saline water over 50 cycles. This work explores the rational design and construction of MXene-based 2D heterostructure and broadens new horizons for the development of novel CDI electrode materials.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

A biomass-rich, self-healable, and high-adhesive polymer binder for advanced lithium-sulfur batteries

Although lithium-sulfur (Li-S) batteries have attracted a great deal of attention due to their ultrahigh energy density, the significant dissolution and shuttle of polysulfides, coupled with the unstable electrode structure, result in a substantial decline in capacity, thereby hindering their practical application in rapidly advancing energy storage systems. In this work, we prepare an environmentally friendly binder (LA-GA) that possesses self-healing abilities and high adhesion by combining dynamic disulfide (SS) bonds with abundant polar functional groups. Significantly, the self-healing capability provided by SS bonds facilitates the repair of cracks resulting from cathode volume expansion. Simultaneously, the polar functional groups (carboxyl and pyrogallol) not only enhance adhesion, preserving cathode integrity, but also effectively participate in lithium polysulfide adsorption, thereby inhibiting the shuttle effect. As a result, sulfur cathodes incorporating the LA-GA binder demonstrate favorable cycling stability, with a high capacity retention of 81.9 % when tested at 0.2C for 100 cycles. Additionally, the long-term cycling performance is satisfactory, showing a small capacity decline rate of 0.0469 % per cycle over 700 cycles at 1.0C.

SnS/SnS2 Heterostructures Embedded in Hierarchical Porous Carbon as Polysulfides Immobilizer for High-Performance Lithium-Sulfur Batteries

Driven by the strong adsorptive and catalytic ability of metal sulfides for soluble polysulfides, it is considered as a potential mediator to resolve the problems of shuttle effect and slow reaction kinetics of polysulfides in lithium-sulfur (Li-S) batteries. However, their further development is limited by poor electrical conductivity and bad long-term durability. Herein, one type of new catalyst composed of SnS/SnS2 heterostructures on hierarchical porous carbon (denoted as SnS/SnS2-HPC) by a simple hydrothermal method is reported and used as an interlayer coating on the conventional separator for blocking polysulfides. The SnS/SnS2-HPC integrates the advantages of a porous conductive network for promoting the transport of electrons and an enhanced electrocatalyst for accelerating polysulfides conversion. As a result, such a cell coupled with a SnS/SnS2-HPC interlayer exhibits a long-term lifespan of 1200 cycles. This work provides a new cell configuration by using heterostructures with a built-in electric field formed from a p-n heterojunction to improve the performance of Li-S batteries.

Exquisitely constructing hierarchical carbon nanoarchitectures decorated with sulfides for high-performance Li-S batteries

The sluggish reaction kinetics and notorious shuttle effect of polysulfides significantly hinder the practical application of lithium-sulfur batteries (LSBs). Therefore, polysulfides are anchored and their conversion reactions are catalyzed to enhance the performance of LSBs. Herein, an exquisite hierarchical carbon nanoarchitecture decorated with sulfides is designed and introduced into LSBs. Systematic experiments show that the nanoarchitecture not only enables rapid electron/ion migration but also functions as an active catalyst to increase polysulfide conversion, thus effectively reducing the shuttle effect. As a result, LSBs with the nanoarchitecture modified separator exhibited outstanding rate capacity (724.9 mA h g-1 at 5C), low self-discharge capacity loss (4.1% capacity loss after 72 h), and exceptional reversible capacity (1518.3 mA h g-1 at 0.1C and 25.6% capacity loss after 100 cycles). Through the design of a multifunctional separator, this study offers an effective way to minimize the shuttle effect and speed up redox conversion. The strategy of constructing nanoarchitectures provides an innovative route for hierarchical heterocatalyst design for LSBs.

A Review on Engineering Transition Metal Compound Catalysts to Accelerate the Redox Kinetics of Sulfur Cathodes for Lithium-Sulfur Batteries

Engineering transition metal compounds (TMCs) catalysts with excellent adsorption-catalytic ability has been one of the most effective strategies to accelerate the redox kinetics of sulfur cathodes. Herein, this review focuses on engineering TMCs catalysts by cation doping/anion doping/dual doping, bimetallic/bi-anionic TMCs, and TMCs-based heterostructure composites. It is obvious that introducing cations/anions to TMCs or constructing heterostructure can boost adsorption-catalytic capacity by regulating the electronic structure including energy band, d/p-band center, electron filling, and valence state. Moreover, the electronic structure of doped/dual-ionic TMCs are adjusted by inducing ions with different electronegativity, electron filling, and ion radius, resulting in electron redistribution, bonds reconstruction, induced vacancies due to the electronic interaction and changed crystal structure such as lattice spacing and lattice distortion. Different from the aforementioned two strategies, heterostructures are constructed by two types of TMCs with different Fermi energy levels, which causes built-in electric field and electrons transfer through the interface, and induces electron redistribution and arranged local atoms to regulate the electronic structure. Additionally, the lacking studies of the three strategies to comprehensively regulate electronic structure for improving catalytic performance are pointed out. It is believed that this review can guide the design of advanced TMCs catalysts for boosting redox of lithium sulfur batteries.

Nonmetallic-Bonding Fe-Mn Diatomic Pairs Anchored on Hollow Carbonaceous Nanodisks for High-Performance Li-S Battery

The issues of polysulfide shuttling and lethargic sulfur redox reaction (SROR) kinetics are the toughest obstacles of lithium-sulfur (Li-S) battery. Herein, integrating the merits of increased density of metal sites and synergistic catalytic effect, a unique single-atom catalyst (SAC) with nonmetallic-bonding Fe-Mn diatomic pairs anchored on hollow nitrogen-doped carbonaceous nanodisk (denoted as FeMnDA@NC) is successfully constructed and well characterized by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, etc. Density functional theory calculation indicates that the Fe-Mn diatomic pairs can effectively inhibit the shuttle effect by enhancing the adsorption ability retarding the polysulfide migration and accelerate the SROR kinetics. As a result, the Li-S battery assembled with FeMnDA@NC modified separator possesses an excellent electrochemical performance with ultrahigh specific capacities of 1419 mAh g-1 at 0.1 C and 885 mAh g-1 at 3.0 C, respectively. An outstanding specific capacity of 1165 mAh g-1 is achieved at 1.0 C and maintains at 731 mAh g-1 after 700 cycles. Notably, the assembled Li-S battery with a high sulfur loading of 5.35 mg cm-2 harvests a practical areal capacity of 5.70 mAh cm-2 at 0.2 C. A new perspective is offered here to construct advanced SACs suitable for the Li-S battery.

Functional MXenes: Progress and Perspectives on Synthetic Strategies and Structure-Property Interplay for Next-Generation Technologies

MXenes are a class of 2D materials that include layered transition metal carbides, nitrides, and carbonitrides. Since their inception in 2011, they have garnered significant attention due to their diverse compositions, unique structures, and extraordinary properties, such as high specific surface areas and excellent electrical conductivity. This versatility has opened up immense potential in various fields, catalyzing a surge in MXene research and leading to note worthy advancements. This review offers an in-depth overview of the evolution of MXenes over the past 5 years, with an emphasis on synthetic strategies, structure-property relationships, and technological prospects. A classification scheme for MXene structures based on entropy is presented and an updated summary of the elemental constituents of the MXene family is provided, as documented in recent literature. Delving into the microscopic structure and synthesis routes, the intricate structure-property relationships are explored at the nano/micro level that dictate the macroscopic applications of MXenes. Through an extensive review of the latest representative works, the utilization of MXenes in energy, environmental, electronic, and biomedical fields is showcased, offering a glimpse into the current technological bottlenecks, such asstability, scalability, and device integration. Moreover, potential pathways for advancing MXenes toward next-generation technologies are highlighted.

Enhanced Electron Delocalization within Coherent Nano-Heterocrystal Ensembles for Optimizing Polysulfide Conversion in High-Energy-Density Li-S Batteries

Commercialization of high energy density Lithium-Sulfur (Li-S) batteries is impeded by challenges such as polysulfide shuttling, sluggish reaction kinetics, and limited Li+ transport. Herein, a jigsaw-inspired catalyst design strategy that involves in situ assembly of coherent nano-heterocrystal ensembles (CNEs) to stabilize high-activity crystal facets, enhance electron delocalization, and reduce associated energy barriers is proposed. On the catalyst surface, the stabilized high-activity facets induce polysulfide aggregation. Simultaneously, the surrounded surface facets with enhanced activity promote Li2 S deposition and Li+ diffusion, synergistically facilitating continuous and efficient sulfur redox. Experimental and DFT computations results reveal that the dual-component hetero-facet design alters the coordination of Nb atoms, enabling the redistribution of 3D orbital electrons at the Nb center and promoting d-p hybridization with sulfur. The CNE, based on energy level gradient and lattice matching, endows maximum electron transfer to catalysts and establishes smooth pathways for ion diffusion. Encouragingly, the NbN-NbC-based pouch battery delivers a Weight energy density of 357 Wh kg-1 , thereby demonstrating the practical application value of CNEs. This work unveils a novel paradigm for designing high-performance catalysts, which has the potential to shape future research on electrocatalysts for energy storage applications.

Enhancing Lithium-Sulfur Battery Performance by MXene, Graphene, and Ionic Liquids: A DFT Investigation

The efficacy of lithium-sulfur (Li-S) batteries crucially hinges on the sulfur immobilization process, representing a pivotal avenue for bolstering their operational efficiency and durability. This dissertation primarily tackles the formidable challenge posed by the high solubility of polysulfides in electrolyte solutions. Quantum chemical computations were leveraged to scrutinize the interactions of MXene materials, graphene (Gr) oxide, and ionic liquids with polysulfides, yielding pivotal binding energy metrics. Comparative assessments were conducted with the objective of pinpointing MXene materials, with a specific focus on d-Ti3C2 materials, evincing augmented binding energies with polysulfides and ionic liquids demonstrating diminished binding energies. Moreover, a diverse array of Gr oxide materials was evaluated for their adsorption capabilities. Scrutiny of the computational outcomes unveiled an augmentation in the solubility of selectively screened d-Ti3C2 MXene and ionic liquids-vis à vis one or more of the five polysulfides. Therefore, the analysis encompasses an in-depth comparative assessment of the stability of polysulfide adsorption by d-Ti3C2 MXene materials, Gr oxide materials, and ionic liquids across diverse ranges.

Application of MXene-Based Materials for Cathode in Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) batteries have a high theoretical specific capacity of 1675 mAh ⋅ g-1 and have become the most promising high-energy storage system for the next generation batteries technology. However, their applications are hindered by insulated feature and volume expansion of sulfur, as well as the "shuttle effect" of polysulfides. MXenes own metallic conductivity and strong ability of polysulfides adsorption. Besides, their unique two-dimensional (2D) structure, large specific surface area, abundant functional groups, and adjustability are beneficial to overcome the drawbacks of the sulfur cathode. In this review, different mainstream preparation methods and excellent properties of MXenes are summarized. Significant achievements and recent progress of MXene-based cathodes and interlayers applied to Li-S cathodes are concluded later. Finally, the challenges, possible solutions and potential applications of MXenes for Li-S batteries are also presented.

Hollow Structure Co1-xS/3D-Ti3C2Tx MXene Composite for Separator Modification of Lithium-Sulfur Batteries

The commercial application of lithium-sulfur (Li-S) batteries has faced obstacles, including challenges related to low sulfur utilization, structural degradation resulting from electrode volume expansion, and migration of polysulfide lithium (LiPSs). Herein, Co1-xS/3D-Ti3C2Tx composites with three-dimensional (3D) multilayered structures are used as separator modification materials for Li-S batteries to solve these problems. The multilevel layered structure of Co1-xS/3D-Ti3C2Tx establishes an efficient electron and Li+ transfer path, alleviates the volume change during the battery charge-discharge process, and enhances the stability of the structure. In addition, the battery assembled with the modified separator shows excellent discharge capacity and cycle stability at 0.5 C and could maintain a high discharge capacity after 500 cycles. This work provides a method for designing highly dispersed metal sulfide nanoparticles on MXenes and extends the application of MXenes-based composites in electrochemical energy storage.

Heterostructures Regulating Lithium Polysulfides for Advanced Lithium-Sulfur Batteries

Sluggish reaction kinetics and severe shuttling effect of lithium polysulfides seriously hinder the development of lithium-sulfur batteries. Heterostructures, due to unique properties, have congenital advantages that are difficult to be achieved by single-component materials in regulating lithium polysulfides by efficient catalysis and strong adsorption to solve the problems of poor reaction kinetics and serious shuttling effect of lithium-sulfur batteries. In this review, the principles of heterostructures expediting lithium polysulfides conversion and anchoring lithium polysulfides are detailedly analyzed, and the application of heterostructures as sulfur host, interlayer, and separator modifier to improve the performance of lithium-sulfur batteries is systematically reviewed. Finally, the problems that need to be solved in the future study and application of heterostructures in lithium-sulfur batteries are prospected. This review will provide a valuable reference for the development of heterostructures in advanced lithium-sulfur batteries.

Enhancing Sulfur Redox Conversion of Active Iron Sites by Modulation of Electronic Density for Advanced Lithium-Sulfur Battery

Despite lithium-sulfur (Li-S) batteries possessing ultrahigh energy density as great promising energy storage devices, the suppressing shuttle effect and improving sulfur redox reaction (SROR) are vital for their practical application. Developing high-activity electrocatalysts for enhancing the SROR kinetics is a major challenge for the application of Li-S batteries. Herein, single-molecule iron phthalocyanine species are anchored on the N and P dual-doped porous carbon nanosheets (Fe-NPPC) via axial Fe-N coordination to optimize the electronic structure of active centers. The Fe-NPPC can promote the catalytic conversion of polysulfides by modulation of the electronic density in active moieties, endowing the Li-S battery with a high reversible capacity of 1023 mAh g-1 at 1 C as well as an ultralow capacity decay of 0.035% per cycle over 1500 cycles. Even with a high sulfur loading of 7.1 mg cm-2 , the Li-S battery delivers a high areal capacity of 4.8 mAh cm-2 after 150 cycles at 0.2 C. With further increasing the sulfur loading to 9.2 mg cm-2 , an excellent areal capacity of up to 9.3 mAh cm-2 is obtained at 0.1 C.

Dual-Defect Engineering of Bidirectional Catalyst for High-Performing Lithium-Sulfur Batteries

Practical applications of lithium-sulfur (Li-S) batteries have been hindered by sluggish reaction kinetics and severe capacity decay during charge-discharge cycling due to the notorious shuttle effect of polysulfide and the unfavored deposition and dissolution of Li2 S. Herein, to address these issues, a double-defect engineering strategy is developed for preparing Co-doped FeP catalyst containing P vacancies on MXene, which effectively improves the bidirectional redox of Li2 S. Mechanism analysis indicates that P vacancy accelerates Li2 S nucleation via increased unsaturated sites, and Co doping generates local electric field to reduce the reaction energy barrier and accelerate Li2 S dissolution. MXene provides highly conductive channels for electron transport, and effectively captures polysulfide. The double-defect catalyst enables an impressive reversible specific capacity of 1297.9 mAh g-1 at 0.2 C, and excellent rate capability of 726.5 mAh g-1 at 4 C. Remarkably, it demonstrates excellent cycling stability with capacity retention of 533.3 mAh g-1 after 500 cycles at 2 C. The results can unlock the double-defect engineering of vacancy induction and heteroatomic doping towards practical Li-S batteries.

Furnishing Continuous Efficient Bidirectional Polysulfide Conversion for Long-Life and High-Loading Lithium-Sulfur Batteries via the Built-In Electric Field

Most catalysts cannot accelerate uninterrupted conversion of polysulfides, resulting in poor long-cycle and high-loading performance of lithium-sulfur (Li-S) batteries. Herein, rich p-n junction CoS2 /ZnS heterostructures embedded on N-doped carbon nanosheets are fabricated by ion-etching and vulcanization as a continuous and efficient bidirectional catalyst. The p-n junction built-in electric field in the CoS2 /ZnS heterostructure not only accelerates the transformation of lithium polysulfides (LiPSs), but also promotes the diffusion and decomposition for Li2 S the from CoS2 to ZnS avoiding the aggregation of lithium sulfide (Li2 S). Meanwhile, the heterostructure possesses a strong chemisorption ability to anchor LiPSs and superior affinity to induce homogeneous Li deposition. The assembled cell with a CoS2 /ZnS@PP separator delivers a cycling stability with a capacity decay of 0.058% per cycle at 1.0 C after 1000 cycles, and a decent areal capacity of 8.97 mA h cm-2 at an ultrahigh sulfur mass loading of 6 mg cm-2 . This work reveals that the catalyst continuously and efficiently converts polysulfides via abundant built-in electric fields to promote Li-S chemistry.

Boosting Lean Electrolyte Lithium-Sulfur Battery Performance with Transition Metals: A Comprehensive Review

Lithium-sulfur (Li-S) batteries have received widespread attention, and lean electrolyte Li-S batteries have attracted additional interest because of their higher energy densities. This review systematically analyzes the effect of the electrolyte-to-sulfur (E/S) ratios on battery energy density and the challenges for sulfur reduction reactions (SRR) under lean electrolyte conditions. Accordingly, we review the use of various polar transition metal sulfur hosts as corresponding solutions to facilitate SRR kinetics at low E/S ratios (< 10 µL mg-1), and the strengths and limitations of different transition metal compounds are presented and discussed from a fundamental perspective. Subsequently, three promising strategies for sulfur hosts that act as anchors and catalysts are proposed to boost lean electrolyte Li-S battery performance. Finally, an outlook is provided to guide future research on high energy density Li-S batteries.

Ethanol-Induced Ni2+ -Intercalated Cobalt Organic Frameworks on Vanadium Pentoxide for Synergistically Enhancing the Performance of 3D-Printed Micro-Supercapacitors

The synthesis of metal-organic framework (MOF) nanocomposites with high energy density and excellent mechanical strength is limited by the degree of lattice matching and crystal surface structure. In this study, dodecahedral ZIF-67 is synthesized uniformly on vanadium pentoxide nanowires. The influence of the coordination mode on the surface of ZIF-67 in ethanol is also investigated. Benefitting from the different coordination abilities of Ni²⁺ , Co²⁺ , and N atoms, spatially separated surface-active sites are created through metal-ion exchange. Furthermore, the incompatibility between the d⁸ electronic configuration of Ni²⁺ and the three-dimensional (3D) structure of ZIF-67 afforded the synthesis of hollow structures by controlling the amount of Ni doping. The formation of NiCo-MOF@CoOOH@V₂ O₅ nanocomposites is confirmed using X-ray absorption fine structure analysis. The high performance of the obtained composite is illustrated by fabricating a 3D-printed micro-supercapacitor, exhibiting a high area specific capacitance of 585 mF cm^-2 and energy density of 159.23 µWh cm^-2 (at power density = 0.34 mW cm^-2 ). The solvent/coordination tuning strategy demonstrated in this study provides a new direction for the synthesis of high-performance nanomaterials for electrochemical energy storage applications.

Dual-Conductive CoSe2 @TiSe2 -C Heterostructures Promoting Overall Sulfur Redox Kinetics under High Sulfur Loading and Lean Electrolyte

Although lithium-sulfur batteries (LSBs) possess a high theoretical specific capacity and energy density, the inherent problems including sluggish sulfur conversion kinetics and the shuttling of soluble lithium polysulfides (LiPSs) have severely hindered the development of LSBs. Herein, cobalt selenide (CoSe₂ ) polyhedrons anchored on few-layer TiSe₂ -C nanosheets derived from Ti₃ C₂ T_x MXenes (CoSe₂ @TiSe₂ -C) are reported for the first time. The dual-conductive CoSe₂ @TiSe₂ -C heterostructures can accelerate the conversion reaction from liquid LiPSs to solid Li₂ S and promote Li₂ S dissociation process through high conductivity and lowered reaction energy barriers for promoting overall sulfur redox kinetics, especially under high sulfur loadings and lean electrolyte. Electrochemical analysis and density functional theory calculation results clearly reveal the catalytic mechanisms of the CoSe₂ @TiSe₂ -C heterostructures from the electronic structure and atomic level. As a result, the cell with CoSe₂ @TiSe₂ -C interlayer maintains a superior cycling performance with 842.4 mAh g^-1  and a low-capacity decay of 0.031% per cycle over 800 cycles at 1.0 C under a sulfur loading of 2.5 mg cm^-2 . More encouragingly, it with a high sulfur loading of ≈7.0 mg cm^-2  still harvests a high areal capacity of ≈6.25 mAh cm^-2  under lean electrolyte (electrolyte/sulfur, E/S ≈ 4.5 µL mg^-1 ) after 50 cycles at 0.05 C.

Metal-Organic Framework Composites and Their Derivatives as Efficient Electrodes for Energy Storage Applications: Recent Progress and Future Perspectives

Metal-organic frameworks (MOFs) have been important electrochemical energy storage (EES) materials because of their rich species, large specific surface area, high porosity and rich active sites. Nevertheless, the poor conductivity, low mechanical and electrochemical stability of pristine MOFs have hindered their further applications. Although single component MOF derivatives have higher conductivity, self-aggregation often occurs during preparation. Composite design can overcome the shortcomings of MOFs and derivatives and create synergistic effects, resulting in improved electrochemical properties for EES. In this review, recent applications of MOF composites and derivatives as electrodes in different types of batteries and supercapacitors are critically discussed. The advantages, challenges, and future perspectives of MOF composites and derivatives have been given. This review may guide the development of high-performance MOF composites and derivatives in the field of EES.

Realizing anti-self-discharged lithium-sulfur batteries by using hierarchical porous carbon nanofibers embedded with Fe/Ni-N catalytic sites

Lithium-sulfur (Li-S) batteries are featured with high gravimetric energy density, yet their commercial application is significantly deteriorated with the severe self-discharging resulted from the polysulfides shuttle and sluggish electrochemical kinetics. Here, a hierarchical porous carbon nanofibers implanted with Fe/Ni-N (denoted as Fe-Ni-HPCNF) catalytic sites are prepared and used as a kinetics booster toward anti-self-discharged Li-S batteries. In this design, the Fe-Ni-HPCNF possesses interconnected porous skeleton and abundant exposed active sites, enabling fast Li-ion conduction, excellent shuttle inhibition and catalytic ability for polysulfides' conversion. Combined with these advantages, this cell with the Fe-Ni-HPCNF equipped separator exhibits an ultralow self-discharged rate of 4.9% after resting for one week. Moreover, the modified batteries deliver a superior rate performance (783.3 mAh g^-1 at 4.0 C) and an outstanding cycling life (over 700 cycles with 0.057% attenuation rate at 1.0 C). This work may guide the advanced design of anti-self-discharged Li-S batteries.

Dual-Functional Hosts for Polysulfides Conversion and Lithium Plating/Stripping towards Lithium-Sulfur Full Cells

The practical application of lithium-sulfur (Li-S) batteries is greatly hindered by the shuttle effect of dissolved polysulfides in the sulfur cathode and the severe dendritic growth in the lithium anode. Adopting one type of effective host with dual-functions including both inhibiting polysulfide dissolution and regulating Li plating/stripping, is recently an emerging research highlight in Li-S battery. This review focuses on such dual-functional hosts and systematically summarizes the recent research progress and application scenarios. Firstly, this review briefly describes the stubborn issues in Li-S battery operations and the sophisticated counter measurements over the challenges by dual-functional behaviors. Then, the latest advances on dual-functional hosts for both cathode and anode in Li-S full cells are catalogued as species, including metal chalcogenides, metal carbides, metal nitrides, heterostuctures, and the possible mechanisms during the process. Besides, we also outlined the theoretical calculation tools for the dual-functional host based on the first principles. Finally, several sound perspectives are also rationally proposed for fundamental research and practical development as guidelines.

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.

Constructing 2D Sandwich-like MOF/MXene Heterostructures for Durable and Fast Aqueous Zinc-Ion Batteries

Two-dimensional metal-organic frameworks (2D MOFs) can be used as the cathodes for high-performance zinc-ion battery due to their large one-dimensional channels. However, the conventionally poor electrical conductivity and low structural stability hinder their advances. Herein, we report an alternately stacked MOF/MX heterostructure, exhibiting the 2D sandwich-like structure with abundant active sites, improved electrical conductivity and exceptional structural stability. Ex situ characterizations and theoretical calculations reveal a reversible intercalation mechanism of zinc ions and high electrical conductivity in the 2D heterostructure. Electrochemical tests confirm excellent Zn²⁺ migration kinetics and ideal pseudocapacitive behaviors. As a consequence, Cu-HHTP/MX shows a superior rate performance (260.1 mAh g^-1 at 0.1 A g^-1 and 173.1 mAh g^-1 at 4 A g^-1 ) and long-term cycling stability of 92.5 % capacity retention over 1000 cycles at 4 A g^-1 .

Interface Engineering Toward Expedited Li2 S Deposition in Lithium-Sulfur Batteries: A Critical Review

Lithium-sulfur batteries (LSBs) with superior energy density are among the most promising candidates of next-generation energy storage techniques. As the key step contributing to 75% of the overall capacity, Li₂ S deposition remains a formidable challenge for LSBs applications because of its sluggish kinetics. The severe kinetic issue originates from the huge interfacial impedances, indicative of the interface-dominated nature of Li₂ S deposition. Accordingly, increasing efforts have been devoted to interface engineering for efficient Li₂ S deposition, which has attained inspiring success to date. However, a systematic overview and in-depth understanding of this critical field are still absent. In this review, the principles of interface-controlled Li₂ S precipitation are presented, clarifying the pivotal roles of electrolyte-substrate and electrolyte-Li₂ S interfaces in regulating Li₂ S depositing behavior. For the optimization of the electrolyte-substrate interface, efforts on the design of substrates including metal compounds, functionalized carbons, and organic compounds are systematically summarized. Regarding the regulation of electrolyte-Li₂ S interface, the progress of applying polysulfides catholytes, redox mediators, and high-donicity/polarity electrolytes is overviewed in detail. Finally, the challenges and possible solutions aiming at optimizing Li₂ S deposition are given for further development of practical LSBs. This review would inspire more insightful works and, more importantly, may enlighten other electrochemical areas concerning heterogeneous deposition processes.

Single Zinc Atom Aggregates: Synergetic Interaction to Boost Fast Polysulfide Conversion in Lithium-Sulfur Batteries

Single-atom catalysts (SACs) pave new possibilities to improve the utilization efficiency of sulfur electrodes arising from polysulfide shuttle effects and sluggish kinetics due to their excellent applicability in atomic-scale reaction mechanisms and structure-activity relationships. Herein, nitrogen (N)-anchored SACs on the highly ordered N-doped carbon nanotube arrays are reported as the sulfur host for fast redox conversion in lithium-sulfur (Li-S) batteries. The cube structure of the aligned carbon nanotubes can promote the rapid mass transfer under high sulfur loadings, and abundant single-atom active sites further accelerate the conversion of lithium polysulfides (LiPSs). The synergistic enhancement effect induced by adjacent single atoms with interatomic distances <1 nm further accelerates the rapid multi-step reaction of sulfur at high sulfur loadings. As a result, the obtained Li-S batteries exhibit outstanding cycle stability with a high areal capacity of 5.6 mAh cm^-2 after 100 cycles under a high sulfur loading of 7.2 mg cm^-2 (electrolyte to sulfur ratio is ≈3.7 mL g^-1 ). Even assembled into a pouch cell, it still delivers a high capacity of 953.4 mAh g^-1 after 100 cycles at 0.1 C, contributing to the development of the practically viable Li-S batteries.

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.

Hoya-like Hierarchical Porous Architecture as Multifunctional Phosphorus Anode for Superior Lithium-Sodium Storage

Designing nanostructured hosts with the merits of high conductivity, strong trapping ability, and long-term durability to improve the insulating nature and extreme volume change of red phosphorus (RP) is a promising option for the development of high-performance lithium/sodium-ion batteries (LIBs/SIBs). Here, a multifunctional RP immobilizer is proposed and fabricated, which comprises a nitrogen-doped hollow MXene sphere (NM) planted with the dual-sided porous carbon network (DCNM). In such a configuration, the highly conductive macroporous NM not only facilitates fast electron transport but also acts as the capturing center to entrap polyphosphide through strong chemical adsorption, while the uniformly distributed micromesoporous carbon network in or out of the sphere provides reliable RP accommodation and alleviates the volume expansion, as well as creates interpenetrating ion diffusion and electron transport channels. Benefiting from the synergistic effect of the triple-shelled architecture and the exclusive restraint, the Hoya-like DCNM@RP anode exhibits significantly enhanced electrochemical performances for LIBs and SIBs, delivering a combination of high reversible capacity, splendid rate properties, and extended cycling performance: up to 1800 cycles with 0.01% per cycle capacity decay for LIBs and 0.024% per cycle over 1000 cycles for SIBs at 2 C.

In situ growth of ZIF-67-derived nickel-cobalt-manganese hydroxides on 2D V2CTx MXene for dual-functional orientation as high-performance asymmetric supercapacitor and electrochemical hydroquinone sensor

Designing dual-functional electrode materials for supercapacitors and pollutant sensors has attracted great interest from researchers for urgent demand in green energy and the environment. In this work, a novel electrode material V2CTx@NiCoMn-OH was successfully constructed for dual-functional orientation via a two-step synthesis strategy, in which the NiCoMn-OH with a three-dimensional (3D) hollow structure was fabricated by employing ZIF-67 as a template and simple anion exchange and composited with the two-dimensional (2D) layered V2CTx MXene. The intercalation of NiCoMn-OH can effectively limit the self-accumulation of V2CTx MXene nanosheets and build a 3D cross-linked hollow structure, thereby broadening the ion transport channel, exposing more active sites of V2CTx@NiCoMn-OH, and simultaneously improving the conductivity of NiCoMn-OH. Benefiting from the unique 3D cross-linked hollow structure, the optimized V2CTx@NiCoMn-OH-20 electrode material exhibits an excellent specific capacitance of 827.45 C g-1 at 1 A g-1. Furthermore, the electrode material has excellent capacitance retention of 88.44% after 10,000 cycles. Moreover, the V2CTx@NiCoMn-OH-20//AC ASC device displays a high energy density of 88.35 Wh kg-1 as well as high power density of 7500 W kg-1 during operation. Additionally, the V2CTx@NiCoMn-OH-20 exhibited excellent electrocatalytic performance in the detection of hydroquinone, including the low detection limit of 0.559 μM (S/N = 3) and the wide linear range of 2-1050 μM. Therefore, the prepared V2CTx@NiCoMn-OH-20 has great potential applications in the fields of supercapacitors and hydroquinone sensors.