Confined Assembly of Asymmetric Block‐Copolymer Nanofibers via Multiaxial Jet Electrospinning

Multiaxial (triaxial/coaxial) electrospinning is utilized to fabricate block copolymer (poly(styrene‐b‐isoprene), PS‐b‐PI) nanofibers covered with a silica shell. The thermally stable silica shell allows post‐fabrication annealing of the fibers to obtain equilibrium self‐assembly. For the case of coaxial nanofibers, block copolymers with different isoprene volume fractions are studied to understand the effect of physical confinement and interfacial interaction on self‐assembled structures. Various confined assemblies such as co‐existing cylinders and concentric lamellar rings are obtained with the styrene domain next to the silica shell. This confined assembly is then utilized as a template to guide the placement of functional nanoparticles such as magnetite selectively into the PI domain in self‐assembled nanofibers. To further investigate the effect of interfacial interaction and frustration due to the physically confined environment, triaxial configuration is used where the middle layer of the self‐assembling material is sandwiched between the innermost and outermost silica layers. The results reveal that confined block‐copolymer assembly is significantly altered by the presence and interaction with both inner and outer silica layers. When nanoparticles are incorporated into PS‐b‐PI and placed as the middle layer, the PI phase with magnetite nanoparticles migrates next to the silica layers. The migration of the PI phase to the silica layers is also observed for the blend of PS and PS‐b‐PI as the middle layer. These materials not only provide a platform to further study the effect of confinement and wall interactions on self‐assembly but can also help develop an approach to fabricate multilayered, multistructured nanofibers for high‐end applications such as drug delivery.     

Polyphenol‐Inspired Facile Construction of Smart Assemblies for ATP‐ and pH‐Responsive Tumor MR/Optical Imaging and Photothermal Therapy

Smart assemblies have attracted increased interest in various areas, especially in developing novel stimuli‐responsive theranostics. Herein, commercially available, natural tannic acid (TA) and iron oxide nanoparticles (Fe₃O₄ NPs) are utilized as models to construct smart magnetic assemblies based on polyphenol‐inspired NPs–phenolic self‐assembly between NPs and TA. Interestingly, the magnetic assemblies can be specially disassembled by adenosine triphosphate, which shows a stronger affinity to Fe₃O₄ NPs than that of TA and partly replaces the surface coordinated TA. The disassembly can further be facilitated by the acidic environment hence causing the remarkable change of the transverse relaxivity and potent “turn‐on” of fluorescence (FL) signals. Therefore, the assemblies for specific and sensitive tumor magnetic resonance and FL dual‐modal imaging and photothermal therapy after intravenous injection of the assemblies are successfully employed. This work not only provides understandings on the self‐assembly between NPs and polyphenols, but also will open new insights for facilely constructing versatile assemblies and extending their biomedical applications.     

Electrical Conductivity,Selective Adhesion,and Biocompatibility in Bacteria‐Inspired Peptide–Metal Self‐Supporting Nanocomposites

Bacterial type IV pili (T4P) are polymeric protein nanofibers that have diverse biological roles. Their unique physicochemical properties mark them as a candidate biomaterial for various applications, yet difficulties in producing native T4P hinder their utilization. Recent effort to mimic the T4P of the metal‐reducing Geobacter sulfurreducens bacterium led to the design of synthetic peptide building blocks, which self‐assemble into T4P‐like nanofibers. Here, it is reported that the T4P‐like peptide nanofibers efficiently bind metal oxide particles and reduce Au ions analogously to their native counterparts, and thus give rise to versatile and multifunctional peptide–metal nanocomposites. Focusing on the interaction with Au ions, a combination of experimental and computational methods provides mechanistic insight into the formation of an exceptionally dense Au nanoparticle (AuNP) decoration of the nanofibers. Characterization of the thus‐formed peptide–AuNPs nanocomposite reveals enhanced thermal stability, electrical conductivity from the single‐fiber level up, and substrate‐selective adhesion. Exploring its potential applications, it is demonstrated that the peptide–AuNPs nanocomposite can act as a reusable catalytic coating or form self‐supporting immersible films of desired shapes. The films scaffold the assembly of cardiac cells into synchronized patches, and present static charge detection capabilities at the macroscale. The study presents a novel T4P‐inspired biometallic material.     

Controllable N‐Doped CuCo2O4@C Film as a Self‐Supported Anode for Ultrastable Sodium‐Ion Batteries

Rational synthesis of flexible electrodes is crucial to rapid growth of functional materials for energy‐storage systems. Herein, a controllable fabrication is reported for the self‐supported structure of CuCo₂O₄ nanodots (≈3 nm) delicately inserted into N‐doped carbon nanofibers (named as 3‐CCO@C); this composite is first used as binder‐free anode for sodium‐ion batteries (SIBs). Benefiting from the synergetic effect of ultrasmall CuCo₂O₄ nanoparticles and a tailored N‐doped carbon matrix, the 3‐CCO@C composite exhibits high cycling stability (capacity of 314 mA h g^?1 at 1000 mA g^?1 after 1000 cycles) and high rate capability (296 mA h g^?1, even at 5000 mA g^?1). Significantly, the Na storage mechanism is systematically explored, demonstrating that the irreversible reaction of CuCo₂O₄, which decomposes to Cu and Co, happens in the first discharge process, and then a reversible reaction between metallic Cu/Co and CuO/Co₃O₄ occurrs during the following cycles. This result is conducive to a mechanistic study of highly promising bimetallic‐oxide anodes for rechargeable SIBs.     

Binary Superlattices from {Mo132} Polyoxometalates and Maghemite Nanocrystals: Long‐Range Ordering and Fine‐Tuning of Dipole Interactions

In the present article, the successful coassembly of spherical 6.2 nm maghemite (γ‐Fe₂O₃) nanocrystals and giant polyoxometalates (POMs) such as 2.9 nm {Mo₁₃₂} is demonstrated. To do so, colloidal solutions of oleic acid‐capped γ‐Fe₂O₃ and long‐chain alkylammonium‐encapsulated {Mo₁₃₂} dispersed in chloroform are mixed together and supported self‐organized binary superlattices are obtained upon the solvent evaporation on immersed substrates. Both electronic microscopy and small angles X‐ray scattering data reveal an AB‐type structure and an enhanced structuration of the magnetic nanocrystals (MNCs) assembly with POMs in octahedral interstices. Therefore, {Mo₁₃₂} acts as an efficient binder constituent for improving the nanocrystals ordering in 3D films. Interestingly, in the case of didodecyldimethylammonium (C₁₂)‐encapsulated POMs, the long‐range ordered binary assemblies are obtained while preserving the nanocrystals magnetic properties due to weak POMs–MNCs interactions. On the other hand, POMs of larger effective diameter can be employed as spacer blocks for MNCs as shown by using {Mo₁₃₂} capped with dioctadecyldimethylammonium (C₁₈) displaying longer chains. In that case, it is shown that POMs can also be used for fine‐tuning the dipolar interactions in γ‐Fe₂O₃ nanocrystal assemblies.     

Electrical characteristics of oxygen doped DNA molecules

In this work, we investigated the possibility of carrier doping of various types of DNA molecules including poly(dG)-poly(dC), DNA poly(dA)-poly(dT) and lambda DNA molecules at low temperatures (i.e., room temperature, 90, 100, and 130 °C) using a rapid thermal annealing processor. N₂ and O₂ were used as doping gasses. Annealing at low temperatures in a vacuum (i.e., without gas doping) was also performed to clarify the roles of both gas sources and heat treatment. The results of this study show that both O₂ doping and heat treatment have certain roles in changing the conduction properties of DNA molecules. Specifically, the conductivity of poly(dG)-poly(dC) molecules increases as the annealing temperature rises, regardless of the gas type. However, the highest value of conductivity at a given annealing temperature was always obtained with the samples annealed at O₂ ambient, suggesting that O₂ doping is more effective at making p-type semiconductor-like poly(dG)-poly(dC) molecules. In contrast, O₂ doping of poly(dA)-poly(dT) and lambda DNA molecules resulted in reduced conductivity. This phenomenon suggests that poly(dA)-poly(dT) and lambda DNA molecules behave like n-type semiconductors due to O₂ doping.     

WO3 Nanofiber‐Based Biomarker Detectors Enabled by Protein‐Encapsulated Catalyst Self‐Assembled on Polystyrene Colloid Templates

A novel catalyst functionalization method, based on protein‐encapsulated metallic nanoparticles (NPs) and their self‐assembly on polystyrene (PS) colloid templates, is used to form catalyst‐loaded porous WO₃ nanofibers (NFs). The metallic NPs, composed of Au, Pd, or Pt, are encapsulated within a protein cage, i.e., apoferritin, to form unagglomerated monodispersed particles with diameters of less than 5 nm. The catalytic NPs maintain their nanoscale size, even following high‐temperature heat‐treatment during synthesis, which is attributed to the discrete self‐assembly of NPs on PS colloid templates. In addition, the PS templates generate open pores on the electrospun WO₃ NFs, facilitating gas molecule transport into the sensing layers and promoting active surface reactions. As a result, the Au and Pd NP‐loaded porous WO₃ NFs show superior sensitivity toward hydrogen sulfide, as evidenced by responses (R_air/R_gas) of 11.1 and 43.5 at 350 °C, respectively. These responses represent 1.8‐ and 7.1‐fold improvements compared to that of dense WO₃ NFs (R_air/R_gas = 6.1). Moreover, Pt NP‐loaded porous WO₃ NFs exhibit high acetone sensitivity with response of 28.9. These results demonstrate a novel catalyst loading method, in which small NPs are well‐dispersed within the pores of WO₃ NFs, that is applicable to high sensitivity breath sensors.     

Ultrafast Growth and Locomotion of Dandelion‐Like Microswarms with Tubular Micromotors

Dynamic assembly and cooperation represent future frontiers for next generations of advanced micro/nano robots, but the required local interaction and communication cannot be directly translated from macroscale robots through the minimization because of tremendous technological challenges. Here, an ultrafast growth and locomotion methodology is presented for dandelion‐like microswarms assembled from catalytic tubular micromotors. With ultrasound oscillation of self‐generated bubbles, such microswarms could overcome the tremendous and chaotic drag force from extensive and disordered bubble generation in single units. Tubular MnO₂ micromotor individuals headed by self‐generated oxygen bubbles are ultrasonically driven to swim rapidly in surfactant‐free H₂O₂ solutions. A large bubble core fused from multiple microbubbles is excited to oscillate and the resultant local intensified acoustic field attracts the individual micromotors to school around it, leading to a simultaneous growth of dandelion‐like microswarms. The bubble‐carried micromotor groups driven by ultrasound could swarm at a zigzag pattern with an average speed of up to 50 mm s^?1, which is validated in low H₂O₂ concentrations. Additionally, such superfast locomotion could be ultrasonically modulated on demand. The ultrafast microswarm growth and locomotion strategy offers a new paradigm for constructing distinct dynamic assemblies and rapid transmission of artificial microrobots, paving the way to a myriad of promising applications.     

Multi‐Component Organic Layers on Metal Substrates

Increasingly high hopes are being placed on organic semiconductors for a variety of applications. Progress along these lines, however, requires the design and growth of increasingly complex systems with well‐defined structural and electronic properties. These issues have been studied and reviewed extensively in single‐component layers, but the focus is gradually shifting towards more complex and functional multi‐component assemblies such as donor–acceptor networks. These blends show different properties from those of the corresponding single‐component layers, and the understanding on how these properties depend on the different supramolecular environment of multi‐component assemblies is crucial for the advancement of organic devices. Here, our understanding of two‐dimensional multi‐component layers on solid substrates is reviewed. Regarding the structure, the driving forces behind the self‐assembly of these systems are described. Regarding the electronic properties, recent insights into how these are affected as the molecule's supramolecular environment changes are explained. Key information for the design and controlled growth of complex, functional multicomponent structures by self‐assembly is summarized.     

Biocatalytically Triggered Co‐Assembly of Two‐Component Core/Shell Nanofibers

For the development of applications and novel uses for peptide nanostructures, robust routes for their surface functionalization, that ideally do not interfere with their self‐assembly properties, are required. Many existing methods rely on covalent functionalization, where building blocks are appended with functional groups, either pre‐ or post‐assembly. A facile supramolecular approach is demonstrated for the formation of functionalized nanofibers by combining the advantages of biocatalytic self‐assembly and surfactant/gelator co‐assembly. This is achieved by enzymatically triggered reconfiguration of free flowing micellar aggregates of pre‐gelators and functional surfactants to form nanofibers that incorporate and display the surfactants’ functionality at the surface. Furthermore, by varying enzyme concentration, the gel stiffness and supramolecular organization of building blocks can be varied.     

Controlling the Diameters of Nanotubes Self‐Assembled from Designed Peptide Bolaphiles

Controlling the diameters of nanotubes represents a major challenge in nanostructures self‐assembled from templating molecules. Here, two series of bolaform hexapeptides are designed, with Set I consisting of Ac‐KI₄K‐NH₂, Ac‐KI₃NleK‐NH₂, Ac‐KI₃LK‐NH₂ and Ac‐KI₃TleK‐NH₂, and Set II consisting of Ac‐KI₃VK‐NH₂, Ac‐KI₂V₂K‐NH₂, Ac‐KIV₃K‐NH₂ and Ac‐KV₄K‐NH₂. In Set I, substitution for Ile in the C‐terminal alters its side‐chain branching, but the hydrophobicity is retained. In Set II, the substitution of Val for Ile leads to the decrease of hydrophobicity, but the side‐chain β‐branching is retained. The peptide bolaphiles tend to form long nanotubes, with the tube shell being composed of a peptide monolayer. Variation in core side‐chain branching and hydrophobicity causes a steady shift of peptide nanotube diameters from more than one hundred to several nanometers, thereby achieving a reliable control over the underlying molecular self‐assembling processes. Given the structural and functional roles of peptide tubes with varying dimensions in nature and in technological applications, this study exemplifies the predictive templating of nanostructures from short peptide self‐assembly.     

Patterning Graphene Surfaces with Iron‐Oxide‐Embedded Mesoporous Polypyrrole and Derived N‐Doped Carbon of Tunable Pore Size

This study develops a novel strategy, based on block copolymer self‐assembly in solution, for preparing two‐dimensional (2D) graphene‐based mesoporous nanohybrids with well‐defined large pores of tunable sizes, by employing polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) spherical micelles as the pore‐creating template. The resultant 2D nanohybrids possess a sandwich‐like structure with Fe₂O₃ nanoparticle‐embedded mesoporous polypyrrole (PPy) monolayers grown on both sides of reduced graphene oxide (rGO) nanosheets (denoted as mPPy‐Fe₂O₃@rGO). Serving as supercapacitor electrode materials, the 2D ternary nanohybrids exhibit controllable capacitive performance depending on the pore size, with high capacitance (up to 1006 F/g at 1 A/g), good rate performance (750 F/g at 20 A/g) and excellent cycling stability. Furthermore, the pyrolysis of mPPy‐Fe₂O₃@rGO at 800 °C yields 2D sandwich‐like mesoporous nitrogen‐doped carbon/Fe₃O₄/rGO (mNC‐Fe₃O₄@rGO). The mNC‐Fe₃O₄@rGO nanohybrids with a mean pore size of 12 nm show excellent electrocatalytic activity as an oxygen reduction reaction (ORR) catalyst with a four‐electron transfer nature, a high half‐wave‐potential of +0.84 V and a limiting current density of 5.7 mA/cm², which are well comparable with those of the best commercial Pt/C catalyst. This study takes advantage of block copolymer self‐assembly for the synthesis of 2D multifunctional mesoporous nanohybrids, and helps to understand the control of their structures and electrochemical performance.     

Morphology‐Controlled Synthesis of SnO2 Nanotubes by Using 1D Silica Mesostructures as Sacrificial Templates and Their Applications in Lithium‐Ion Batteries

SnO₂ nanotubes with controllable morphologies are successfully synthesized by using a variety of one‐dimensional (1D) silica mesostructures as effective sacrificial templates. Firstly, 1D silica mesostructures with different morphologies, such as chiral nanorods, nonchiral nanofibers, and helical nanotubes, are readily synthesized in aqueous solution by using the triblock copolymer Pluronic F127 and the cationic surfactant cetyltrimethylammonium bromide as binary templates. Subsequently, the obtained 1D silica mesostructures are used as sacrificial templates to synthesize SnO₂ nanotubes with preserved morphologies via a simple hydrothermal route, resulting in the formation of well‐defined SnO₂ nanotubes with different lengths and unique helical SnO₂ nanotubes with a wealth of conformations. It is revealed that both of the short and long SnO₂ nanotubes showed much better performance as anode materials in lithium‐ion batteries than normal SnO₂ nanopowders, which might be related to the hollow structure of the nanotubes that could alleviate the volume changes and mechanical stress during charging/discharging cycling. Moreover, the capacity and cycling performance of short nanotubes, which showed a specific discharge capacity of 468 mAh g^?1 after 30 cycles, are considerably better than those of long nanotubes because of the more robust structure of the short nanotubes.     

Solvent‐Induced Self‐Assembly Strategy to Synthesize Well‐Defined Hierarchically Porous Polymers

Porous polymers with well‐orchestrated nanomorphologies are useful in many fields, but high surface area, hierarchical structure, and ordered pores are difficult to be satisfied in one polymer simultaneously. Herein, a solvent‐induced self‐assembly strategy to synthesize hierarchical porous polymers with tunable morphology, mesoporous structure, and microporous pore wall is reported. The poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) diblock copolymer micelles are cross‐linked via Friedel–Crafts reaction, which is a new way to anchor micelles into porous polymers with well‐defined structure. Varying the polarity of the solvent has a dramatic effect upon the oleophobic/oleophylic interaction, and the self‐assembly structure of PEO‐b‐PS can be tailored from aggregated nanoparticles to hollow spheres even mesoporous bulk. A morphological phase diagram is accomplished to systematically evaluate the influence of the composition of PEO‐b‐PS and the mixed solvent component on the pore structure and morphology of products. The hypercrosslinked hollow polymer spheres provide a confined microenvironment for the in situ reduction of K₂PdCl₄ to ultrasmall Pd nanoparticles, which exhibit excellent catalytic performance in solvent‐free catalytic oxidation of hydrocarbons and alcohols.     

Stable Low‐Current Electrodeposition of α‐MnO2 on Superaligned Electrospun Carbon Nanofibers for High‐Performance Energy Storage

Metal oxide/carbonaceous nanomaterials are promising candidates for energy‐storage applications. However, inhomogeneous mass and charge transfer across the electrode/electrolyte interface due to unstable metal oxide/carbonaceous nanomaterial synthesis limit their performance in supercapacitors. Here, it is shown that the above problems can be mitigated through stable low‐current electrodeposition of MnO₂ on superaligned electrospun carbon nanofibers (ECNFs). The key to this approach is coupling a self‐designed four steel poles collector for aligned ECNFs and a constant low‐current (40 µA) electrodeposition technique to form a uniform Na⁺‐induced α‐MnO₂ film which proceeds by a time‐dependent growth mechanism involving cluster‐“kebab” structures and ending with a compact, uniform MnO₂ film for high‐performance energy storage.     

Two‐Step Assembly of Thermoresponsive Gold Nanorods Coated with a Single Kind of Ligand

Gold nanorods (GNRs) coated with a single kind of ligand show thermoreponsive two‐step assembly to provide a hierarchical structure. The GNRs (33 nm in length × 14 nm in diameter) coated with a hexa(ethylene glycol) (HEG) derivative form side‐by‐side assemblies at 30 °C (T_A1) as a steady state through dehydration. By further heating to over 40 °C (T_A2), larger assemblies, which are composed of the side‐by‐side assembled units, are formed as hierarchical structures. The dehydration temperature of the HEG derivative varies depending on the free volume of the HEG unit, which corresponds to the curvature of the GNRs. Upon heating, dehydration first occurs from the ligands on the side portions with a lower curvature, and then from the ligands on the edge portions with a higher curvature. The different sized GNRs (33 × 8 and 54 × 15 nm) also show two‐step assembly. Both the T_A1 and T_A2 are dependent on the diameter of the GNRs, but independent of their length. This result supports that the dehydration is dependent on the free volume, which corresponds to the curvature. Anisotropic assembly focusing on differences in curvature provides new guidelines for the fabrication of hierarchical structures.     

Multifunctional POSS‐Based Nano‐Photo‐Initiator for Overcoming the Oxygen Inhibition of Photo‐Polymerization and for Creating Self‐Wrinkled Patterns

Oxygen inhibition remains a challenge in photo‐curing technology despite the expenditure of considerable effort in developing a convenient, efficient, and low‐cost prevention method. Here, a novel strategy to prevent oxygen inhibition is presented; it is based on the self‐assembly of multifunctional nano‐photo‐initiators (F₂‐POSS‐(SH)₄‐TX/EDB) at the interface of air and the liquid monomer. These nano‐photo‐initiators consist of a thiol‐containing polyhedral oligomeric silsesquioxane (POSS) skeleton onto which fluorocarbon chains and thioxanthone and dimethylaminobenzoate (TX/EDB) photo‐initiator moieties are grafted. Real‐time Fourier‐transform infrared spectroscopy (FT‐IR) is used to investigate the photo‐polymerization of various acrylate monomers that are initiated by F₂‐POSS‐(SH)₄‐TX/EDB and its model analogues in air and in N₂. FT‐IR results show that F₂‐POSS‐(SH)₄‐TX/EDB decreases the effects of oxygen inhibition. X‐ray photo‐electron spectroscopy and atomic force microscopy reveal that the self‐assembly of F₂‐POSS‐(SH)₄‐TX/EDB at the air/(liquid monomer) interface forms a cross‐linked top layer via thiol–ene polymerization; this layer acts as a physical barrier against the diffusion of oxygen from the surface into the bulk layer. A mismatch in the shrinkage between the top and bulk layers arise as a result of the different types of photo‐cross‐linking reactions. Subsequently, the surface develops a wrinkled pattern with a low surface energy. This strategy exhibits considerable potential for preventing oxygen inhibition, and the wrinkled pattern may prove very useful in photo‐curing technology.     

Li+‐Containing,Continuous Silica Nanofibers for High Li+ Conductivity in Composite Polymer Electrolyte

Solid‐state electrolytes have recently attracted significant attention toward safe and high‐energy lithium chemistries. In particular, polyethylene oxide (PEO)‐based composite polymer electrolytes (CPEs) have shown outstanding mechanical flexibility and manufacturing feasibility. However, their limited ionic conductivity, poor electrochemical stability, and insufficient mechanical strength are yet to be addressed. In this work, a novel CPE supported by Li⁺‐containing SiO₂ nanofibers is developed. The nanofibers are obtained via sol–gel electrospinning, during which lithium sulfate is in situ introduced into the nanofibers. The uniform doping of Li₂SO₄ in SiO₂ nanofibers increases the Li⁺ conductivity of SiO₂, generates mesopores on the surface of SiO₂ nanofibers, and improves the wettability between SiO₂ and PEO. As a result, the obtained SiO₂/Li₂SO₄/PEO CPE yields high Li⁺ conductivity (1.3 × 10^?4 S cm^?1 at 60 °C, ≈4.9 times the Li₂SO₄‐free CPE) and electrochemical stability. Furthermore, the all‐solid‐state LiFePO₄‐Li full cell demonstrates stable cycling with high capacities (over 80 mAh g^?1, 50 cycles at C/2 at 60 °C). The Li⁺‐containing mesoporous SiO₂ nanofibers show great potential as the filler for CPEs. Similar methods can be used to incorporate Li salts into other filler materials for CPEs.     

Temperature‐Enhanced Solvent Vapor Annealing of a C3 Symmetric Hexa‐peri‐Hexabenzocoronene: Controlling the Self‐Assembly from Nano‐ to Macroscale

Temperature‐enhanced solvent vapor annealing (TESVA) is used to self‐assemble functionalized polycyclic aromatic hydrocarbon molecules into ordered macroscopic layers and crystals on solid surfaces. A novel C₃ symmetric hexa‐peri‐hexabenzocoronene functionalized with alternating hydrophilic and hydrophobic side chains is used as a model system since its multivalent character can be expected to offer unique self‐assembly properties and behavior in different solvents. TESVA promotes the molecule's long‐range mobility, as proven by their diffusion on a Si/SiO_x surface on a scale of hundreds of micrometers. This leads to self‐assembly into large, ordered crystals featuring an edge‐on columnar type of arrangement, which differs from the morphologies obtained using conventional solution‐processing methods such as spin‐coating or drop‐casting. The temperature modulation in the TESVA makes it possible to achieve an additional control over the role of hydrodynamic forces in the self‐assembly at surfaces, leading to a macroscopic self‐healing within the adsorbed film notably improved as compared to conventional solvent vapor annealing. This surface re‐organization can be monitored in real time by optical and atomic force microscopy.     

Okra‐Like Fe7S8/C@ZnS/N‐C@C with Core–Double‐Shelled Structures as Robust and High‐Rate Sodium Anode

Core–multishelled structures with controlled chemical composition have attracted great interest due to their fascinating electrochemical performance. Herein, a metal–organic framework (MOF)‐on‐MOF self‐templated strategy is used to fabricate okra‐like bimetal sulfide (Fe₇S₈/C@ZnS/N‐C@C) with core–double‐shelled structure, in which Fe₇S₈/C is distributed in the cores, and ZnS is embedded in one of the layers. The MOF‐on‐MOF precursor with an MIL‐53 core, a ZIF‐8 shell, and a resorcinol–formaldehyde (RF) layer (MIL‐53@ZIF‐8@RF) is prepared through a layer‐by‐layer assembly method. After calcination with sulfur powder, the resultant structure has a hierarchical carbon matrix, abundant internal interface, and tiered active material distribution. It provides fast sodium‐ion reaction kinetics, a superior pseudocapacitance contribution, good resistance of volume changes, and stepwise sodiation/desodiation reaction mechanism. As an anode material for sodium‐ion batteries, the electrochemical performance of Fe₇S₈/C@ZnS/N‐C@C is superior to that of Fe₇S₈/C@ZnS/N‐C, Fe₇S₈/C, or ZnS/N‐C. It delivers a high and stable capacity of 364.7 mAh g^?1 at current density of 5.0 A g^?1 with 10 000 cycles, and registers only 0.00135% capacity decay per cycle. This MOF‐on‐MOF self‐templated strategy may provide a method to construct core–multishelled structures with controlled component distributions for the energy conversion and storage.