Hierarchical Nanocapsules of Cu-Doped MoS2@H-Substituted Graphdiyne for Magnesium Storage

Tailored Polypyrrole Nanofibers as Ion-to-Electron Transduction Membranes for Wearable K+ Sensors

Conductive polymers are recognized as ideal candidates for the development of noninvasive and wearable sensors for real-time monitoring of potassium ions (K+) in sweat to ensure the health of life. However, the low ion-to-electron transduction efficiency and limited active surface area hamper the development of high-performance sensors for low-concentration K+ detection in the sweat. Herein, a wearable K+ sensor is developed by tailoring the nanostructure of polypyrrole (PPy), serving as an ion-to-electron transduction layer, for accurately and stably tracing the K+ fluctuation in human sweat. The PPy nanostructures can be tailored from nanospheres to nanofibers by controlling the supramolecular assembly process during PPy polymerization. Resultantly, the ion-to-electron transduction efficiency (17-fold increase in conductivity) and active surface area (1.3-fold enhancement) are significantly enhanced, accompanied by minimized water layer formation. The optimal PPy nanofibers-based K+ sensor achieved a high sensitivity of 62 mV decade-1, good selectivity, and solid stability. After being integrated with a temperature sensor, the manufactured wearable sensor realized accurate monitoring of K+ fluctuation in the human sweat.

Synergistic Cathode Design for High-Performance Dual-Salt Magnesium/Lithium-Ion Batteries Using 2D/2D 1T/2H-MoS2@Ti3C2Tx MXene Nanocomposite

Magnesium-ion batteries (MIBs) and dual-salt magnesium/lithium-ion batteries (MLIBs) have emerged as promising contenders for next-generation energy storage. In contrast to lithium metal anode in lithium metal batteries, magnesium metal anode in MIBs and MLIBs presents a safer alternative due to the limited dendrite growth and higher volumetric capacity, along with higher natural abundance. This study explores a MLIB configuration with a novel cathode design by employing a 2D/2D nanocomposite of 1T/2H mixed phase MoS2 and delaminated Ti3C2Tx MXene (1T/2H-MoS2@MXene) to address challenges associated with slow kinetics of magnesium ions during cathode interactions. This cathode design takes advantage of the high electrical conductivity of Ti3C2Tx MXene and the expanded interlayer spacing with enhanced conductivity of the 1T metallic phase in 1T/2H mixed phase MoS2. Through a designed synthesis method, the resulting nanocomposite cathode maintains structural integrity, enabling the stable and reversible storage of dual Mg2+ and Li+ ions. The nanocomposite cathode demonstrates superior performance in MLIBs compared to individual components (253 mAh g-1 at 50 mA g-1, and 36% of capacity retention at 1,000 mA g-1), showcasing short ion transport paths and fast ion storage kinetics. This work represents a significant advancement in cathode material design for cost-effective and safe MLIBs.

Multiscale Structural Design of 2D Nanomaterials-based Flexible Electrodes for Wearable Energy Storage Applications

2D nanomaterials play a critical role in realizing high-performance flexible electrodes for wearable energy storge devices, owing to their merits of large surface area, high conductivity and high strength. The electrode is a complex system and the performance is determined by multiple and interrelated factors including the intrinsic properties of materials and the structures at different scales from macroscale to atomic scale. Multiscale design strategies have been developed to engineer the structures to exploit full potential and mitigate drawbacks of 2D materials. Analyzing the design strategies and understanding the working mechanisms are essential to facilitate the integration and harvest the synergistic effects. This review summarizes the multiscale design strategies from macroscale down to micro/nano-scale structures and atomic-scale structures for developing 2D nanomaterials-based flexible electrodes. It starts with brief introduction of 2D nanomaterials, followed by analysis of structural design strategies at different scales focusing on the elucidation of structure-property relationship, and ends with the presentation of challenges and future prospects. This review highlights the importance of integrating multiscale design strategies. Finding from this review may deepen the understanding of electrode performance and provide valuable guidelines for designing 2D nanomaterials-based flexible electrodes.

Mechanistic exploration of Co doping in optimizing the electrochemical performance of 2H-MoS2/N-doped carbon anode for potassium-ion battery

The 2H-MoS2/nitrogen-doped carbon (2H-MoS2/NC) composite is a promising anode material for potassium-ion batteries (PIBs). Various transition metal doping has been adopted to optimize the poor intrinsic electronic conductivity and lack of active sites in the intralayer of 2H-MoS2. However, its optimization mechanisms have not been well probed. In this paper, using Cobalt (Co) as an example, we aim to investigate the influence of transition metal doping on the electronic and mechanical properties and electrochemical performance of 2H-MoS2/NC via first-principles calculation. Co doping is found to be effective in improving the electronic conductivity and the areas of active sites on different positions (C surface, interface, and MoS2 surface) of 2H-MoS2/NC. The increased active sites can optimize K adsorption and diffusion capability/processes, where general smaller K adsorption energies and diffusion energy barriers are found after Co doping. This helps improve the rate performance. Especially, the pyridinic N (pyN), pyrrolic N (prN), and graphitic N (grN) are first unveiled to respectively work best in K kinetic adsorption, diffusion, and interfacial stability. These findings are instructive to experimental design of high rate 2H-MoS2/NC electrode materials. The roles of different N types provide new ideas for optimal design of other functional composite materials.

1T-2H Mixed-Phase MoS2 Stabilized with a Hyperbranched Polyethylene Ionomer for Mg2+ /Li+ Co-Intercalation Toward High-Capacity Dual-Salt Batteries

Dual-salt magnesium/lithium-ion batteries (MLIBs) benefit from fast lithium ion diffusion on the cathode side while providing safety due to the dendrite-free Mg2+ stripping/plating mechanism on the anode side. Bulk MoS2 (B-MoS2 ), as a cathode for magnesium-ion batteries (MIBs), suffers from low conductivity and relatively van der Waals gaps and, consequently, resists against divalent Mg2+ insertion due to the high Coulombic interactions. In MLIBs, it exhibits a Daniell-cell type mechanism with the sole accommodation of Li+ . In this paper, the synthesis of a 1T/2H mixed-phase MoS2 (MP-MoS2 ) modified with a hyperbranched polyethylene ionomer, I@MP-MoS2 , for high-capacity MLIBs with a distinct Mg2+ /Li+ co-intercalation mechanism is reported. Benefiting from the enhanced conductivity (due to 53% metallic 1T phase), expanded van der Waals gaps (79% expansion compared to B-MoS2 , 1.11 vs 0.62 nm), and enhanced interactions with THF-based electrolytes following the modification, I@MP-MoS2 shows a dramatically increased Mg2+ storage compared to its parent analogue (144 mAh g-1 vs ≈2 mAh g-1 at 20 mA g-1 ). In MLIBs, I@MP-MoS2 is demonstrated to exhibit remarkable specific capacities up to ≈270 mAh g-1 at 20 mA g-1 through a Mg2+ /Li+ co-intercalation mechanism with 87% of capacity retention over 200 cycles at 100 mA g-1 .

Anion-substitution interfacial engineering to construct C@MoS2 hierarchical nanocomposites for broadband electromagnetic wave absorption

Developing an effective strategy to regulate the interfacial properties of hierarchical structure is of great significance for preparation of high-performance electromagnetic wave absorption (EMA) materials. Ion-substitution can change intrinsic structure and properties of a materials, but its effect on the interfacial properties of hierarchical structure remained to be explored. Herein, we first constructed a C@MoS2 hierarchical structure via simple hydrothermal reaction, then used the ion-substitution strategy to replace the S atoms in MoS2 with O, F and Se, and finally obtained anion-substituted hierarchical structure (C@X-MoS2, X = O, F, Se). The results show that ion-substitution destroys the MoS2 crystal structure and realizes tunable dielectric properties of C@MoS2, which leads to further enhancement of overall interfacial polarization. After optimization, the absorption strength and width of C@O-MoS2 has been significantly improved. The minimum reflection loss (RLmin) reaches -62.17 dB, and the maximum effective absorption bandwidth (EABmax) is 7.0 GHz. The simulation results show the obtained absorbent can greatly reduce the radar cross section of target, indicating it has broad application potential. Therefore, this work provides a novel method for regulation of EMA performance of hierarchical structure and preparation of high-performance absorbents.

Engineering Single-Layer Hollow Structure of Transition Metal Dichalcogenides with High 1T-Phase Purity for Hydrogen Evolution Reaction

Rational design and controllable synthesis of hollow structures based on transition metal dichalcogenides (TMDs) have gained tremendous attention in the field of clean energy. However, the general synthetic strategies to fabricate single-layer hollow structures of TMDs, especially with unconventional phases (e.g., 1T or 1T'), still pose significant challenges. Herein, a scalable method is reported for the synthesis of single-layer hollow spheres (SLHS) of TMDs with high 1T-phase purity by etching bismuth (Bi) cores from pre-synthesized Bi@TMDs core-shell heterostructures including SLHS-1T-MoS2 , SLHS-1T-MoSe2 , SLHS-1T-WS2 , and SLHS-1T-WSe2 . Additionally, the etched Bi ions can be adsorbed on the single-layer TMDs shells in the form of single atoms (SAs) via the Bi─S bond. Due to the benefits of the single-layer hollow structure, high conductivity of 1T phase, and synergistic effect of Bi SAs and TMDs supports, the fabricated SLHS-1T-MoS2 exhibits superior electrocatalytic performance for hydrogen production. This work provides a way to manufacture advanced functional materials based on the single-layer hollow structures of 1T-TMDs and to expand their applications.

Implanting CuS Quantum Dots into Carbon Nanorods for Efficient Magnesium-Ion Batteries

Magnesium-ion batteries (MIBs) are emerging as potential next-generation energy storage systems due to high security and high theoretical energy density. Nevertheless, the development of MIBs is limited by the lack of cathode materials with high specific capacity and cyclic stability. Currently, transition metal sulfides are considered as a promising class of cathode materials for advanced MIBs. Herein, a template-based strategy is proposed to successfully fabricate metal-organic framework-derived in-situ porous carbon nanorod-encapsulated CuS quantum dots (CuS-QD@C nanorods) via a two-step method of sulfurization and cation exchange. CuS quantum dots have abundant electrochemically active sites, which facilitate the contact between the electrode and the electrolyte. In addition, the tight combination of CuS quantum dots and porous carbon nanorods increases the electronic conductivity while accelerating the transport speed of ions and electrons. With these architectural and compositional advantages, when used as a cathode material for MIBs, the CuS-QD@C nanorods exhibit remarkable performance in magnesium storage, including a high reversible capacity of 323.7 mAh g-1 at 100 mA g-1 after 100 cycles, excellent long-term cycling stability (98.5 mAh g-1 after 1000 cycles at 1.0 A g-1 ), and satisfying rate performance (111.8 mA g-1 at 1.0 A g-1 ).

Interfacial Engineering of Bimetallic Ni/Co-MOFs with H-Substituted Graphdiyne for Ammonia Electrosynthesis from Nitrate

The electrochemical synthesis of ammonia is highly dependent on the coupling reaction between nitrate and water, for which an electrocatalyst with a multifunctional interface is anticipated to promote the deoxygenation and hydrogenation of nitrate with water. Herein, by engineering the surface of bimetallic Ni/Co-MOFs (NiCoBDC) with hydrogen-substituted graphdiyne (HsGDY), a hybrid nanoarray of NiCoBDC@HsGDY with a multifunctional interface has been achieved toward scale-up of the nitrate-to-ammonia conversion. On the one hand, a partial electron transfers from Ni²⁺ to the coordinatively unsaturated Co²⁺ on the surface of NiCoBDC, which not only promotes the deoxygenation of *NO₃ on Co²⁺ but also activates the water-dissociation to *H on Ni²⁺. On the other hand, the conformal coated HsGDY facilitates both electrons and NO₃^- ions gathering on the interface between NiCoBDC and HsGDY, which moves forward the rate-determining step from the deoxygenation of *NO₃ to the hydrogenation of *N with both *H on Ni²⁺ and *H₂O on Co²⁺. As a result, such a NiCoBDC@HsGDY nanoarray delivers high NH₃ yield rates with Faradaic efficiency above 90% over both wide potential and pH windows. When assembled into a galvanic Zn-NO₃^- battery, a power density of 3.66 mW cm^-2 is achieved, suggesting its potential in the area of aqueous Zn-based batteries.

Hybrid nanoarrays of Cu-MOFs@H-substituted graphdiyne with various levels of Lewis acidity for nitrate electroreduction

To mimic enzymes in nature, a set of hybrid nanoarrays of Cu-MOFs sealed in hydrogen-substituted graphdiyne has been developed in order to serve as Lewis-acid-promoted catalysts. By regulating the electron-withdrawing capability of the ligands bridging Cu²⁺ sites, these Cu-MOFs provided different levels of Lewis acidity toward nitrate affinity, a feature crucial for nitrate-to-ammonia conversion.

Redispersion mechanisms of 2D nanosheets: combined role of intersheet contact and surface chemistry

Redispersion behavior recovers the important features of nanomaterials and thus holds great promise for exciting applications of nanomaterials in different fields. In contrast to the redispersion of nanoparticles, which is mainly determined by surface chemistry, the redispersion of 2D nanosheets could be more complicated and is not well understood. In the present study, the redispersion behavior of 2D NMs was investigated by selecting representative nanosheets, MoS₂, graphene oxide and their derivatives with both experimental methods and molecular dynamics (MD) simulations. The good agreement between experiments and MD simulations suggested that the redispersion in response to surface chemistry was regulated by the alignment configurations of the nanosheets. More importantly, we revealed that the difference in the hydrophilicity properties is responsible for the distinctive separation distances of the 1T and 2H MoS₂ nanosheets. Appropriately adjusting the alignment configuration of the nanosheets can alter the effect of surface hydrophilicity on the redispersion behavior. Based on these fundamental findings, we identified three distinctive zones for the redispersion tendency of the 2D nanosheets with different surface hydrophilicity, Hamaker constants and intersheet contacts. As one of the implications, the results serve as a prescreening for the stability of the 2D restacking-based membrane. For the first time, the study systematically reported the interplay of intersheet configuration and surface chemistry in the redispersion of nanosheets, which provides a theoretical foundation for the processing and applications of 2D nanomaterials.

Photocurrent-Polarity-Switching Photoelectrochemical Biosensor for Switching Spatial Distance Electroactive Tags

This work presents a photocurrent-polarity-switching-based photoelectrochemical (PEC) biosensing platform for ultrasensitive detection of microRNA-21 (miR-21) through target-triggered catalytic hairpin assembly (CHA) for modulation of methylene blue (MB) and ferrocene (Fc) positional configurations using double-shelled Cu-doped ZnS nanocages (NCs)-Au nanoparticles (NPs) as photoactive materials. In the presence of miR-21, the assembly of MB-labeled HP1 and Fc-labeled HP2 leads to the generation of a large amount of double-stranded DNA (HP1-HP2), which pushes MB away from the electrode surface and brings Fc close to the electrode surface, resulting in effectively quenching the enhanced PEC signal to activate the photocurrent-polarity-switching system. Benefiting from the distance-controllable strategy, the designed PEC bioanalysis can effectively eliminate false-positive and false-negative signals due to the change of different signal expression patterns (from traditional the "signal-on" mode to the photocurrent-polarity-switching mode), thereby significantly improving the sensing specificity and sensitivity. The proposed PEC sensing system exhibited satisfying photocurrent responses toward target miR-21 within the working range from 1.0 fM to 1 nM at a low limit of detection (LOD) of 0.58 fM. More importantly, we demonstrated the successful integration of the proposed PEC biosensor with a handheld wireless device for instant detection of miR-21 concentrations in practical samples.

Pseudocapacitive Vanadium Nitride Quantum Dots Modified One-Dimensional Carbon Cages Enable Highly Kinetics-Compatible Sodium Ion Capacitors

The kinetics incompatibility between battery-type anode and capacitive-type cathode for sodium ion hybrid capacitors (SIHCs) seriously hinders their overall performance output. Herein, we construct a SIHCs device by coupling with quantum grade vanadium nitride (VN) nanodots anchored in one-dimensional N/F co-doped carbon nanofiber cages hybrids (VNQDs@PCNFs-N/F) as the freestanding anode and the corresponding activated N/F co-doped carbon nanofiber cages (APCNFs-N/F) as cathode. The strong coupling of VN quantum dots with N/F co-doped 1D conductive carbon cages effectively facilitates the ion/electron transport and intercalation-conversion-deintercalation reactions, ensuring fast sodium storage to surmount aforesaid kinetics incompatibility. Additionally, density functional theory calculations cogently manifest that the abundant active sites in the VNQDs@PCNFs-N/F configuration boost the Na⁺ adsorption/reaction activity well which will promote both "intrinsic" and "extrinsic" pseudocapacitance and further improve anode kinetics. Consequently, the assembled SIHCs device can achieve high energy densities of 157.1 and 95.0 Wh kg^-1 at power densities of 198.8 and 9100.5 W kg^-1, respectively, with an ultralong cycling life over 8000 cycles. This work further verified the feasibility of kinetics-compatible electrode design strategy toward metal ion hybrid capacitors.

Recent Progress in Phase Regulation, Functionalization, and Biosensing Applications of Polyphase MoS2

The disulfide compounds of molybdenum (MoS₂ ) are layered van der Waals materials that exhibit a rich array of polymorphic structures. MoS₂ can be roughly divided into semiconductive phase and metallic phase according to the difference in electron filling state of the 4d orbital of Mo atom. The two phases show completely different properties, leading to their diverse applications in biosensors. But to some extent, they compensate for each other. This review first introduces the relationship between phase state and the chemical/physical structures and properties of MoS₂ . Furthermore, the synthetic methods are summarized and the preparation strategies for metastable phases are highlighted. In addition, examples of electronic and chemical property designs of MoS₂ by means of doping and surface modification are outlined. Finally, studies on biosensors based on MoS₂ in recent years are presented and classified, and the roles of MoS₂ with different phases are highlighted. This review offers references for the selection of materials to construct different types of biosensors based on MoS₂ , and provides inspiration for sensing performance enhancement.

Designing anisotropic inorganic nanocapsules via self-assembly of polymer-like ultrathin Au nanowires

Anisotropic assembly of nanomaterials into hollow structures is an attractive technique in biomedicine and biosensing. Commonly used polymer materials are easy to assemble yet it is hard to form anisotropic morphologies. Here in this work, we successfully prepared a novel gold nanocapsule with an anisotropic ellipsoidal shape and cavity structure by the self-assembly of ultrathin Au nanowires. The assembly mechanism is further studied by tuning the assembly conditions such as nanowire concentration, solvent composition, and temperature. It is found that the controlling forces of the nanowire assembly process are mainly the symmetric interfacial tension and the asymmetric nanowire deformation potential, which contribute together to result in anisotropic nanocapsules. Finally, the obtained Au nanocapsules were used as nanocarriers to load pyrene as a model drug, showing great drug loading ability and pH-responsive drug release behavior. We believe that this unique anisotropic assembly product will bring new insights into nanostructure design and soft matter research.

Core-Shell-Structured Carbon Nanotube@VS4 Nanonecklaces as a High-Performance Cathode Material for Magnesium-Ion Batteries

As a typical layered transition metal chalcogenide, VS₄ is considered as a promising cathode material for advanced magnesium-ion batteries. However, the poor electronic conductivity and severe polarization effect restrict its practical applications. Herein, we report a betaine-assisted solvothermal strategy to coat VS₄ nanoblocks on the surface of carbon nanotubes (CNTs), obtaining unique core-shell-structured CNT@VS₄ nanonecklaces. As a result of the morphology-controlling effect of betaine, VS₄ exhibits an unusual nanoblock morphology, which renders abundant active sites and promotes the contact between the electrode and electrolyte. CNTs serve as a highly conductive skeleton, combining with the VS₄ nanoblocks and ensuring their uniform distribution. As a benefit from the synergistic effect of abundant active sites and electron-conductive highways, the as-synthesized CNT@VS₄ nanonecklaces manifest remarkable performance for magnesium storage, including a large reversible capacity of 170 mAh g^-1 at 0.1 A g^-1, outstanding cycle stability (76.3 mAh g^-1 after 800 cycles at 0.5 A g^-1), and superior rate performance (77.2 mAh g^-1 at 2 A g^-1).