Nitrogen-Doped Metallic MoS2 Derived from a Metal-Organic Framework for Aqueous Rechargeable Zinc-Ion Batteries

Enhancing aqueous zinc-ion battery performance through a dual-mechanism strategy

The development of a high capacity electrode in aqueous rechargeable zinc ion batteries has attracted extensive interest. Herein, ammonium molybdenum sulfide hydrate (N-MoSx) nanospheres containing S-S bonds are reported. The N-MoSx/Zn system exhibits a high reversible capacity of 135.64 mA h g-1 and excellent long-term cyclability. Moreover, an interesting dual mechanism with insertion of Zn2+ and the breakage/formation of disulfide bonds is demonstrated.

Honeycomb-like MnO/C hybrids with strong interfacial interactions for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have garnered significant attention for large-scale energy storage applications due to their high theoretical capacity, low cost, and inherent safety. However, the absence of cathode materials exhibiting superior electrochemical performance severely impedes their further development. In this study, we report a metal-organic framework (MOF)-derived honeycomb-like MnO/C hybrid as a high-performance cathode material for AZIBs. A facile synthesis method was employed to uniformly embed MnO nanoparticles within a carbon matrix, thereby forming a honeycomb-like structure with robust heterointerfaces. This unique architecture provides efficient pathways for ion and electron transport, significantly enhancing structural stability and electrochemical performance. The MnO/C hybrid exhibits a high discharge specific capacity of 388 mA h g-1 at a current density of 50 mA g-1 and demonstrates excellent cycling stability, with a capacity decay rate of only 0.01% per cycle over 1000 cycles at a high current density of 2000 mA g-1. Comprehensive material characterization and electrochemical testing reveal the underlying mechanisms responsible for the superior electrochemical performance. This work provides a new perspective on the development of high-performance manganese-based cathode materials for AZIBs.

Insights into Interlayer Dislocation Augmented Zinc-Ion Storage Kinetics in MoS2 Nanosheets for Rocking-Chair Zinc-Ion Batteries with Ultralong Cycle-Life

Increasing attention to sustainability and cost-effectiveness in energy storage sector has catalyzed the rise of rechargeable Zinc-ion batteries (ZIBs). However, finding replacement for limited cycle-life Zn-anode is a major challenge. Molybdenum disulfide (MoS2), an insertion-type 2D layered material, has shown promising characteristics as a ZIB anode. Nevertheless, its high Zn-ion diffusion barrier because of limited interlayer spacing substantiates the need for interlayer modifications. Here, N-doped carbon quantum dots (N-CQDs) are used to modify the interlayers of MoS2, resulting in increased interlayer spacing (0.8 nm) and rich interlayer dislocations. MoS2@N-CQDs attain a high specific capacity (258 mAh g-1 at 0.1 A g-1), good cycle life (94.5% after 2000 cycles), and an ultrahigh diffusion coefficient (10-6 to 10-8 cm2 s-1), much better than pristine MoS2. Ex situ Raman studies at charge/discharge states reveal that the N-CQDs-induced interlayer expansion and dislocations can reversibly accommodate the volume strain created by Zn-ion diffusion within MoS2 layers. Atomistic insight into the interlayer dislocation-induced Zn-ion storage of MoS2 is unveiled by molecular dynamic simulations. Finally, rocking-chair ZIB with MoS2@N-CQDs anode and a ZnxMnO2 cathode is realized, which achieved a maximum energy density of 120.3 Wh kg-1 and excellent cyclic stability with 97% retention after 15 000 cycles.

Design and Regulation of Anthraquinone's Electrochemical Properties in Aqueous Zinc-Ion Batteries via Benzothiadiazole and Its Dinitro Derivatives

Organic cathode materials are widely considered as highly promising for aqueous zinc-ion batteries (AZIBs) due to their tunable properties, low cost, and ease of processing and synthesis. Benzothiadiazoles have demonstrated significant potential as organic electrode materials in AZIBs, owing to their strong electron-accepting capabilities and the presence of multiple reversible redox sites in anthraquinone. In this study, we designed a polymer, poly(2-methyl-6-(7-methyl-5,6-dinitrobenzo[c][1,2,5]thiadiazol-4-yl)anthracene-9,10-dione) (PBDQ), with multielectron transfer capability through a copolymerization approach. Additionally, we synthesized another polymer, poly2,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)anthracene-9,10-dione(PBDQ-N), by introducing two electron-withdrawing nitro groups on the aromatic ring of benzothiadiazole. The introduction of nitro groups, with their unique electronic properties, enhances electron delocalization and increases the number of electrochemically active sites, thereby promoting faster zinc-ion insertion/extraction reactions. Experimental results show that both PBDQ and PBDQ-N exhibit excellent electrochemical properties due to the abundance of active sites and extended π-conjugation. Among them, PBDQ-N demonstrates outstanding performance, including an ultrahigh specific capacity of 446.2 mAh g-1 at 0.1 A g-1 and excellent cycle life exceeding 20,000 cycles at 10 A g-1. Moreover, the lower lowest-unoccupied molecular orbital (LUMO) energy level and improved conductivity of PBDQ-N provide a fast electron transfer rate, resulting in a higher Zn2+ diffusion coefficient (3.47 × 10-11-2.6 × 10-8 cm2 s-1) and exceptional rate performance (234.6 mAh g-1 at 10 A g-1). Theoretical calculations and ex situ characterizations confirm that C═O, C═N, and N═O groups all participate as active sites in Zn2+ storage. This work highlights how molecular design and the introduction of functional groups, such as nitro groups, can effectively regulate the electrochemical properties of organic polymers in AZIBs. It also demonstrates the impact of these strategies on the electrochemical performances of these materials when they are used as cathodes in aqueous zinc-ion batteries.

Interlayer Space Engineering-Induced Pseudocapacitive Zinc-Ion Storage in Holey Graphene Oxide-Bearing Vertically Oriented MoS2 Nano-Wall Array Cathode for Aqueous Rechargeable Zn Metal Batteries

Transition metal dichalcogenides, particularly MoS2, are acknowledged as a promising cathode material for aqueous rechargeable zinc metal batteries (ARZMBs). Nevertheless, its lack of hydrophilicity, poor electrical conductivity, significant restacking, and restricted interlayer spacing translate into inadequate capacity and rate performance. Herein, the unique porous structure and additional functional groups present in holey graphene oxide (hGO) are taken advantage of to dictate the vertical growth pattern of oxygen-doped MoS2 nanowalls (O-MoS2/NW) over the hGO surface. Compared to conventional graphene oxide (GO), the presence of nano-pores in hGO facilitates the homogeneous dispersion of Mo precursors and provides stronger interaction sites, promoting the uniform vertical alignment of O-MoS2/NW. The synergistic interaction between O-MoS2-NW and hGO translates to enhanced electron conductivity, efficient electrolyte penetration, enhanced interlayer spacing, reduced restacking, and enhanced surface area. As a consequence of precise control of various factors that decide the overall battery performance, a high discharge capacity (227 mAh g-1 at 100 mA g-1) cathode material with significantly lower charge transfer resistance (66 Ω) compared to pristine O-MoS2 (153 Ω) is developed. These findings underscore the potential of hGO as a multifunctional platform for nanoengineering high-performance cathode materials for the next generation of efficient and durable ARZMBs.

Photo-Assisted Chemical Self-Rechargeable Zinc Ion Batteries with High Charging and Discharging Efficiency

Chemical self-recharging zinc ion batteries (ZIBs), which are capable of auto-recharging in ambient air, are promising in self-powered battery systems. Nevertheless, the exclusive reliance on chemical energy from oxygen for ZIBs charging often would bring some obstacles in charging efficiency. Herein, we develop photo-assisted chemical self-recharging aqueous ZIBs with a heterojunction of MoS2/SnO2 cathode, which are favorable to enhancing both the charging and discharging efficiency as well as the chemical self-charging capabilities under illumination. The photo-assisted process promotes the electron transfer from MoS2/SnO2 to oxygen, accelerating the occurrence of the oxidation reaction during chemical self-charging. Furthermore, the electrons within the MoS2/SnO2 cathode exhibit a low transfer impedance under illumination, which is beneficial to reducing the migration barrier of Zn2+ within the cathode and thereby facilitating the uniform inserting of Zn2+ into MoS2/SnO2 cathode during discharging. This photo-assisted chemical self-recharging mechanism enables ZIBs to attain a maximum self-charging potential of 0.95 V within 3 hours, a considerable self-charging capacity of 202.5 mAh g-1 and excellent cycling performance in a self-charging mode. This work not only provides a route for optimizing chemical self-charging energy storage, but also broadens the potential application of aqueous ZIBs.

Nitrogen doped 1 T/2H mixed phase MoS2/CuS heterostructure nanosheets for enhanced peroxidase activity

Heteroatom doping and phase engineering are effective ways to promote the catalytic activity of nanoenzymes. Nitrogen-doped 1 T/2H mixed phase MoS2/CuS heterostructure nanosheets N-1 T/2H-MoS2/CuS are prepared by a simple hydrothermal approach using polyoxometalate (POM)-based metal-organic frameworks (MOFs) (NENU-5) as a precursor and urea as nitrogen doping reagent. The XPS spectroscopy (XPS) and Raman spectrum of N-1 T/2H-MoS2/CuS prove the successful N-doping. NENU-5 was used as the template to prepare 1 T/2H-MoS2/CuS with high content of 1 T phase by optimizing the reaction time. The use of urea as nitrogen dopant added to 1 T/2H-MoS2/CuS, resulted in N-1 T/2H-MoS2/CuS with an increase in the content of the 1 T phase from 80 % to 84 % and higher number of defects. N-1 T/2H-MoS2/CuS shows higher peroxidase activity than 1 T/2H-MoS2/CuS and a catalytic efficiency (Kcat/Km) for H2O2 twice as high as that of 1 T/2H-MoS2/CuS. The enhanced catalytic activity has probably been attributed to several reasons: (i) the insertion of urea during the hydrothermal process in the S-Mo-S layer of MoS2, causing an increase in the interlayer spacing and in 1 T phase content, (ii) the replacement of S atoms in MoS2 by N atoms from the urea decomposition, resulting in more defects and more active sites. As far as we know, N-1 T/2H-MoS2/CuS nanosheets have the lowest detection limit (0.16 µm) for the colorimetric detection of hydroquinone among molybdenum disulfide-based catalysts. This study affords a new approach for the fabrication of high-performance nanoenzyme catalysts.

In Situ Molecular Engineering Strategy to Construct Hierarchical MoS2 Double-Layer Nanotubes for Ultralong Lifespan "Rocking-Chair" Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc ion batteries (AZIBs) have gained considerable attention owing to their low cost and high safety, but dendrite growth, low plating/stripping efficiency, surface passivation, and self-erosion of the Zn metal anode are hindering their application. Herein, a one-step in situ molecular engineering strategy for the simultaneous construction of hierarchical MoS2 double-layer nanotubes (MoS2-DLTs) with expanded layer-spacing, oxygen doping, structural defects, and an abundant 1T-phase is proposed, which are designed as an intercalation-type anode for "rocking-chair" AZIBs, avoiding the Zn anode issues and therefore displaying a long cycling life. Benefiting from the structural optimization and molecular engineering, the Zn2+ diffusion efficiency and interface reaction kinetics of MoS2-DLTs are enhanced. When coupled with a homemade ZnMn2O4 cathode, the assembled MoS2-DLTs//ZnMn2O4 full battery exhibited impressive cycling stability with a capacity retention of 86.6% over 10 000 cycles under 1 A g-1anode, outperforming most of the reported "rocking-chair" AZIBs. The Zn2+/H+ cointercalation mechanism of MoS2-DLTs is investigated by synchrotron in situ powder X-ray diffraction and multiple ex situ characterizations. This research demonstrates the feasibility of MoS2 for Zn-storage anodes that can be used to construct reliable aqueous full batteries.

Molecular modulation strategies for two-dimensional transition metal dichalcogenide-based high-performance electrodes for metal-ion batteries

In the past few decades, great efforts have been made to develop advanced transition metal dichalcogenide (TMD) materials as metal-ion battery electrodes. However, due to existing conversion reactions, they still suffer from structural aggregation and restacking, unsatisfactory cycling reversibility, and limited ion storage dynamics during electrochemical cycling. To address these issues, extensive research has focused on molecular modulation strategies to optimize the physical and chemical properties of TMDs, including phase engineering, defect engineering, interlayer spacing expansion, heteroatom doping, alloy engineering, and bond modulation. A timely summary of these strategies can help deepen the understanding of their basic mechanisms and serve as a reference for future research. This review provides a comprehensive summary of recent advances in molecular modulation strategies for TMDs. A series of challenges and opportunities in the research field are also outlined. The basic mechanisms of different modulation strategies and their specific influences on the electrochemical performance of TMDs are highlighted.

MoSe2 hollow nanospheres with expanded selenide interlayers for high-performance aqueous zinc-ion batteries

Transition metal dichalcogenides (TMDs) as materials for aqueous zinc-ion batteries (ZIBs) have received a lot of interest because of their large theoretical capacity and unique layered structure. However, the sluggish kinetics and inferior cyclic stability limit the usefulness of ZIBs. In the present investigation, the interlayer spacing enlarged MoSe2 hollow nanospheres comprised of nanosheets with ultrathin shells have been successfully synthesized through a combined strategy of template assistance and anion-exchange reaction. The hierarchical ultrathin nanosheets and hollow structure effectively suppress the agglomeration of pure nanosheets and ameliorate volume fluctuations induced by ion migration during (dis)charging/charging. The interlayer expansion provides good channels for the transport of Zn2+ ions and speeds up the insertion/extraction of Zn2+. In addition, in-situ carbon modification can significantly improve electronic conductivity. Therefore, the electrode prepared from MoSe2 hollow nanospheres with enlarged interlayer spacing not only exhibits outstanding cycle stability (capacity retention of 94.5% after 1600 cycles) but also exhibits high-rate capability (266.1 mA h g-1 at 0.1 A g-1 and 203.6 mA h g-1 at 3 A g-1). This work could provide new insights into the design of cathode using TMDs of hollow structure for Zn2+ storage.

A topochemical reaction induced the formation of Bi2S3 micro-straws from a Bi-MOF for an ultra-long Zn storage life

Aqueous zinc ion batteries (ZIBs) are considered as promising energy storage devices in the post-lithium-ion era, due to their high energy density, low cost, high safety, and environmental benignity, however their commercialization is hindered by the sluggish diffusion kinetics of cathode materials due to the large hydrate Zn2+ radius. In this work, we propose a unique structure inheritance strategy for preparing Bi2S3 micro-straws in which a metal-organic framework (MOF) denoted as Bi-PYDC (PYDC2- = 3,5-pyridinedicarboxylate) with a string of [Bi2O2]2+ chains is judiciously selected as the structure-directing template to induce the formation of micro-straws based on a topochemical reaction. The distinctive hollow structure significantly enhances the ionic storage kinetics. Impressively, the obtained battery exhibits an ultra-long cycle life of more than 10 000 cycles at a current density of 1 A g-1 while maintaining a capacity of more than 153.4 mA h g-1. In addition, the Zn2+ insertion/extraction mechanism of Bi2S3 micro-straws is also investigated by multiple analytical methods, revealing the involvement of Zn2+ rather than H+ in the electrochemical storage process. This work may lead a new direction for constructing high performance cathodes of Zn-ion batteries through a MOF-based structure-directing template.

Interfacial engineering of transition metal dichalcogenide/carbon heterostructures for electrochemical energy applications

To support the global goal of carbon neutrality, numerous efforts have been devoted to the advancement of electrochemical energy conversion (EEC) and electrochemical energy storage (EES) technologies. For these technologies, transition metal dichalcogenide/carbon (TMDC/C) heterostructures have emerged as promising candidates for both electrode materials and electrocatalysts over the past decade, due to their complementary advantages. It is worth noting that interfacial properties play a crucial role in establishing the overall electrochemical characteristics of TMDC/C heterostructures. However, despite the significant scientific contribution in this area, a systematic understanding of TMDC/C heterostructures' interfacial engineering is currently lacking. This literature review aims to focus on three types of interfacial engineering, namely interfacial orientation engineering, interfacial stacking engineering, and interfacial doping engineering, of TMDC/C heterostructures for their potential applications in EES and EEC devices. To accomplish this goal, a combination of experimental and theoretical approaches was used to allow the analysis and summary of the fundamental electrochemical properties and preparation strategies of TMDC/C heterostructures. Moreover, this review highlights the design and utilization of the interfacial engineering of TMDC/C heterostructures for specific EES and EEC devices. Finally, the challenges and opportunities of using interfacial engineering of TMDC/C heterostructures in practical EES and EEC devices are outlined. We expect that this review will effectively guide readers in their understanding, design, and application of interfacial engineering of TMDC/C heterostructures.

Crystal water intercalated interlayer expanded MoS2 nanosheets as a cathode for efficient zinc-ion storage

Zinc-ion batteries (ZIBs) have attracted tremendous interest from the scientific community in recent years due to their extreme safety, cost-effectiveness, environmental benignity and the unique properties of the Zn anode. However, more suitable cathode materials are needed to achieve their potential widespread applications. MoS2, a 2D layered material with fascinating properties, could also serve as a cathode in ZIBs but is rarely studied due to its limited interlayer spacing, poor ionic/electronic conductivity and hydrophobicity. In this work, we report a facile hydrothermal method for synthesizing crystal water-intercalated MoS2 nanosheets and their application in efficient Zn-ion storage. Morphological characterization reveals the average thickness of the nanosheets to be 15.2 nm. With a large interlayer spacing (0.79 nm), high 1T content (49.7%) and high defects, MoS2·nH2O achieves a high discharge capacity of 197 mA h g-1 at 0.1 A g-1 in an aqueous 2 M ZnSO4 electrolyte. Moreover, it exhibits modest cyclic stability with 55% capacity retention after 1000 charge/discharge cycles. Furthermore, we evaluated the charge storage kinetics of crystal water-intercalated MoS2 nanosheets and realized that the electrochemical reaction is diffusion dominated with a diffusion coefficient of 10-10 to 10-13 cm2 s-1 in a 0.3 to 1.3 V potential window. This simple and cost-effective strategy for improving the performance of ZIBs by crystal water intercalation in 2D cathode materials will pave the way for their commercial-level grid-scale applications.

Vertically aligned MoS2 nanosheets on monodisperse MXene as electrolyte-philic cathodes for zinc ion batteries with enhanced capacity

Zinc ion batteries (ZIBs) have attracted extensive attention for their high safety and environmentally friendly nature, and considerable theoretical capacities. Due to its unique two-dimensional layered structure and high theoretical specific capacities, molybdenum disulfide (MoS₂) presents as a promising cathode material for ZIBs. Nevertheless, the low electrical conductivity and poor hydrophilicity of MoS₂ limits its wide application in ZIBs. In this work, MoS₂/Ti₃C₂T_x composites are effectively constructed using a one-step hydrothermal method, where two-dimensional MoS₂ nanosheets are vertically grown on monodisperse Ti₃C₂T_x MXene layers. Contributing to the high ionic conductivity and good hydrophilicity of Ti₃C₂T_x, MoS₂/Ti₃C₂T_x composites possess improved electrolyte-philic and conductive properties, leading to a reduced volume expansion effect of MoS₂ and accelerated Zn²⁺ reaction kinetics. As a result, MoS₂/Ti₃C₂T_x composites exhibit high voltage (1.6 V) and excellent discharge specific capacity of 277.8 mA h g^-1 at 0.1 A g^-1, as well as cycle stability as cathode materials for ZIBs. This work provides an effective strategy for developing cathode materials with high specific capacity and stable structure.

A three-dimensional interconnected molybdenum disulfide/multi-walled carbon nanotubes cathode with enlarged interlayer spacing for aqueous zinc-ion storage

Layered molybdenum disulfide (MoS₂) shows tremendous prospect as cathode material for aqueous zinc-ion batteries (AZIBs) due to the two-dimensional zinc ions (Zn²⁺) diffusion channels and tunable interlayer spacing. However, it is subjected to sluggish insertion/extraction kinetics, inferior electronic conductivity and inadequate active capacities. Herein, a three-dimensional (3D) interconnected MoS₂/multi-walled carbon nanotubes (MWCNTs) framework is proposed to address these issues. Importantly, the MWCNTs cores offer interconnection routes for fast electrons and zinc ions transport, the expanded spacing of MoS₂ interlayer with 1.05 nm can facilitate rapid Zn²⁺ intercalation/extraction, and the confined MoS₂ layers in inner MWCNTs can mitigate the agglomeration and restacking of MoS₂ nanosheets. Benefitting from the confined structural configuration, sufficient active surface and 3D structural stability, the MoS₂/MWCNTs as AZIBs cathode delivers a large initial reversible capacity of 218.3 mAh/g and high coulombic efficiency of 78.2 % at 0.1 A/g. Additionally, the 3D interconnected cathode maintains nearly intact structure after a fierce galvanostatic charge/discharge process, resulting in large retained capacities of 126.3 mAh/g at 1 A/g after 650 cycles and 101.1 mAh/g at 3 A/g after 1000 cycles. This work offers a novel strategy for the structure design of two-dimensional materials to develop high-performance cathodes for AZIBs.

Stable structure and fast ion diffusion: N-doped VO2 3D porous nanoflowers for applications in ultrafast rechargeable aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion batteries (ARZIBs) are promising candidates for fast-charging energy-storage systems. The issues of stronger interactions between Zn²⁺ and the cathode for ultrafast ARZIBs can be partially addressed by enhancing mass transfer and ion diffusion of the cathode. Herein, via thermal oxidation for the first time, N-doped VO₂ porous nanoflowers with short ion diffusion paths and improved electrical conductivity were synthesized as ARZIBs cathode materials. The introduction of nitrogen derived from the vanadium-based-zeolite imidazolyl framework (V-ZIF) contributes to enhanced electrical conductivity and faster ion diffusion, while the thermal oxidation of the VS₂ precursor assists the final product in exhibiting a more stable three-dimensional nanoflower structure. In particular, the N-doped VO₂ cathode shows excellent cycle stability and superior rate capability with the delivered capacities of 165.02 mAh g^-1 and 85 mAh g^-1, at 10 A g^-1 and 30 A g^-1, and the capacity retention of 91.4% after 2200 cycles and 99% after 9000 cycles, respectively. Remarkably, the battery takes less than 10 s to be fully charged at 30 A g^-1. Hence, this work provides a new avenue for designing unique nanostructured vanadium oxides and developing electrode materials suitable for ultrafast charging.

Enlarged Interlayer Spacing of Marigold-Shaped 1T-MoS2 with Sulfur Vacancies via Oxygen-Assisted Phosphorus Embedding for Rechargeable Zinc-Ion Batteries

Structural unsteadiness and sluggish diffusion of divalent zinc cations in cathodes during cycling severely limit further applications of MoS₂ for rechargeable aqueous zinc-ion batteries (ZIBs). To circumvent these hurdles, herein, phosphorus (P) atom embedded three-dimensional marigold-shaped 1T MoS₂ structures combined with the design of S vacancies (Sv) are synthesized via the oxygen-assisted solvent heat method. The oxygen-assisted method is utilized to aid the P-embedding into the MoS₂ crystal, which can expand the interlayer spacing of P-MoS₂ and strengthen Zn²⁺ intercalation/deintercalation. Meanwhile, the three-dimensional marigold-shaped structure with 1T phase retains the internal free space, can adapt to the volume change during charge and discharge, and improve the overall conductivity. Moreover, Sv is not only conducive to the formation of rich active sites to diffuse electrons and Zn²⁺ but also improves the storage capacity of Zn²⁺. The electrochemical results show that P-MoS₂ can reach a high specific capacity of 249 mAh g^-1 at 0.1 A g^-1. The capacity remains at 102 mAh g^-1 after 3260 cycles at a current of 0.5 A g^-1, showing excellent electrochemical performance for Zn²⁺ ion storage. This research provides a more efficient method of P atom embedded MoS₂-based electrodes and will heighten our comprehension of developing cathodes for the ZIBs.

Hexagonal Carbon Nanoplates Decorated with Layer-Engineered MoS2: High-Performance Cathode Materials for Zinc-Ion Batteries

Hexagonal carbon nanoplates bearing MoS₂ (HCN@MoS₂) were synthesized using two-dimensional (2D) microporous organic polymers as templating materials. The layer number of MoS₂ in HCN@MoS₂ and the 2D morphology of composites were critical factors to achieve high-performance cathode materials for aqueous zinc-ion batteries. The best cathode performance was obtained with HCN@MoS₂ bearing 2-3 layered MoS₂ (HCN@MoS₂-2), showing excellent discharge capacities of 602 mAh/g (@50 mA/g), 498 mAh/g (@0.1 A/g), and 328 mAh/g (@1 A/g). The promising electrochemical performance of HCN@MoS₂-2 is attributable to the facilitated insertion of zinc ions into 2-3 layered MoS₂ due to the reduced lattice energy and the efficient electrochemical utilization of composite materials.

Heterostructures Stimulate Electric-Field to Facilitate Optimal Zn2+ Intercalation in MoS2 Cathode

The electric-field effect is an important factor to enhance the charge diffusion and transfer kinetics of interfacial electrode materials. Herein, by designing a heterojunction, the influence of the electric-field effect on the kinetics of the MoS₂ as cathode materials for aqueous Zn-ion batteries (AZIBs) is deeply investigated. The hybrid heterojunction is developed by hydrothermal growth of MoS₂ nanosheets on robust titanium-based transition metal compound ([titanium nitride, TiN] and [titanium oxide, TiO₂ ]) nanowires, denoted TNC@MoS₂ and TOC@MoS₂ NWS, respectively. Benefiting from the heterostructure architecture and electric-field effect, the TNC@MoS₂ electrodes exhibit an impressive rate performance of 200 mAh g^-1 at 50 mA g^-1 and cycling stability over 3000 cycles. Theoretical studies reveal that the hybrid architecture exhibits a large-scale electric-field effect at the interface between TiN and MoS₂ , enhances the adsorption energy of Zn-ions, and increases their charge transfer, which leads to accelerated diffusion kinetics. In addition, the electric-field effect can also be effectively applied to TiO₂ and MoS₂ , confirming that the concept of heterostructures stimulating electric-field can provide a relevant understanding for the architecture of other cathode materials for AZIBs and beyond.

A strategy for anode modification for future zinc-based battery application

In the past several years, rechargeable zinc batteries, featuring the merits of low cost, environmental friendliness, easy manufacturing, and enhanced safety, have, attracted much attention. Zinc (Zn) anodes for zinc metal batteries play an important role. In this review, the fundamental understanding of these batteries and modification strategies to deal with the problematic issues for Zn anodes, including dendrite growth, corrosion, and the hydrogen evolution phenomenon will be summarized. The practical application of Zn anodes can still lead to Zn dendrites, various side reactions, and serious safety risks. Therefore, metal-free anodes for "rocking chair" zinc ion batteries to replace Zn anodes are systemically reviewed. The performance and the zinc storage mechanism of metal-free anodes will be discussed. Subsequently, a "rocking chair" zinc ion battery prototype selected as a recent example is assessed to explore the merits and demerits of Zn anodes and metal-free anodes. To conclude, a perspective on the future of zinc metal batteries and "rocking chair" zinc ion batteries is presented. It is hoped that this review may provide for further improvement of commercial rechargeable zinc batteries.

Recent Advances of Transition Metal Chalcogenides as Cathode Materials for Aqueous Zinc-Ion Batteries

In recent years, advances in lithium-ion batteries (LIBs) have pushed the research of other metal-ion batteries to the forefront. Aqueous zinc ion batteries (AZIBs) have attracted much attention owing to their low cost, high capacity and non-toxic characteristics. Among various cathodes, transition metal chalcogenides (TMCs) with a layered structure are considered as suitable electrode materials. The large layer spacing facilitates the intercalation/de-intercalation of Zn²⁺ between the layers. In this mini-review, we summarize a variety of design strategies for the modification of TMCs. Then, we specifically emphasize the zinc storage capacity of the optimized electrodes. Finally, we propose the challenges and future prospects of cathode materials for high-energy AZIBs.

Metal-Organic Framework-Based Materials for Aqueous Zinc-Ion Batteries: Energy Storage Mechanism and Function

Aqueous rechargeable zinc-ion batteries (ZIBs) featuring competitive performance, low cost and high safety hold great promise for applications in grid-scale energy storage and portable electronic devices. Metal-organic frameworks (MOFs), relying on their large framework structure and abundant active sites, have been identified as promising materials in ZIBs. This review comprehensively presents the current development of MOF-based materials including MOFs and their derivatives in ZIBs, which begins with Zn storage mechanism of MOFs, followed by introduction of various types of MOF-based cathode materials (PB and PBA, Mn-based MOF, V-based MOF, conductive MOF and their derivatives), and the regulation approaches for Zn deposition behavior. The key factors and optimization strategies of MOF-based materials that affect ZIBs performance are emphasized and discussed. Finally, the challenges and further research directions of MOF-based materials for advanced zinc-ion batteries are provided.

N-Doped MoS2 Nanoflowers for Efficient Cr(VI) Removal

The removal of Cr(VI) has attracted extensive attention since it causes serious harm to public health. Herein, we report a two-step method to synthesize N-doped MoS₂ nanoflowers (NFs) with controllable sizes, which are first utilized for Cr(VI) removal and display outstanding removal performance. The N-MoS₂ NFs with an average size of 40 nm (N-MoS₂ NFs-40 nm) can rapidly remove Cr(VI) in 15 min under optimal conditions. The maximum adsorption capacity of N-MoS₂ NFs-40 nm can reach 787.41 mg·g^-1, which is significantly larger than that of N-MoS₂ NFs-150 and -400 nm (314.46 and 229.88 mg·g^-1). Meanwhile, N-MoS₂ NFs-400 nm have a higher maximum adsorption capacity than pure MoS₂ NFs-400 nm (172.12 mg·g^-1). In this adsorption/reduction process, N-MoS₂ NFs have abundant adsorption sites due to a high surface area. N doping can generate more sulfur vacancy defects in the MoS₂ NF structure to accelerate electron transfer and enhance the reduction of Cr(VI) to low-toxicity Cr(III). This study provides a facile approach to fabricating N-MoS₂ nanoflowers and demonstrates their superior removal ability for Cr(VI).

Hexagonal WO3/3D Porous Graphene as a Novel Zinc Intercalation Anode for Aqueous Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have acquired great attention because of their high safety and environmentally friendly properties. However, the uncontrollable Zn dendrites and the irreversibility of electrodes seriously affect their practical application. Herein, hexagonal WO₃/three-dimensional porous graphene (h-WO₃/3DG) is investigated as an intercalation anode for ZIBs. As a result, the h-WO₃/3DG//Zn half-battery shows excellent electrochemical performance with a high capacity of 115.6 mAh g^-1 at 0.1 A g^-1 and 89% capacity retention at 2.0 A g^-1 after 10 000 cycles. The reason could be that the crystalline structure of WO₃, which has hexagonal channels, with a diameter of 5.36 Å, much higher than the diameter of Zn²⁺ (0.73 Å), accelerating the insertion/extraction of Zn ions. A zinc metal-free full battery using h-WO₃/3DG as the anode and ZnMn₂O₄/carbon black (ZnMn₂O₄/CB) as the cathode is constructed, exhibiting an initial capacity of 66.8 mAh g^-1 at 0.1 A g^-1 corresponding to an energy density of 73.5 W h kg^-1 (based on the total mass of anode and cathode-active materials) and a capacity retention of 76.6% after 1000 cycles at 0.5 A g^-1. This work demonstrates the high potential of hexagonal WO₃ as an advanced intercalation anode material for Zn metal-free batteries and may inspire new ideas for the development of other intercalation anode hosts for ZIBs.

Mg ion pre-intercalated MnO2 nanospheres as high-performance cathode materials for aqueous Zn-ion batteries

Rechargeable Zn-MnO2 batteries with mild and nearly neutral aqueous electrolytes have shown great potential for large-scale energy storage because of their high safety, low cost, environmental friendliness and high energy...