Densely Branched Carbon Nanotubes for Boosting the Electrochemical Performance of Li-S Batteries.

To address the inherent limitations of conventional carbon nanotubes (CNTs), such as their tendency to agglomerate and scarcity of catalytic sites, the development of branched carbon nanotubes (BCNTs) with a unique hierarchical structure has emerged as a promising solution. Herein, gram scale quantities of densely branched and structurally consistent Ni-Fe decorated branched CNTs (Ni-Fe@BCNT) have been prepared. This uniform and densely branched architecture ensures excellent dispersibility and superior electrical conductivity. Additionally, each branched tip is equipped with Ni-Fe particles, thereby providing numerous catalytic sites which endow them with exceptional catalytic activity for the conversion of polysulfides. The polypropylene (PP) separator modified with Ni-Fe@BCNT interlayer is fabricated as a multifunctional barrier for Li-S batteries. The experimental results demonstrate that Ni-Fe@BCNT interlayer can effectively suppress the shuttle effect of polysulfides and enhance their redox kinetics. The outstanding catalytic ability of Ni-Fe@BCNT interlayer enables batteries with high specific capacities, outstanding rate performance, and remarkable cycling stability. This approach proposed in this work paves a new path for synthesizing BCNTs and shows great potential for scaling up the production of BCNTs to address more demanding applications.

Oriented Linear Self-Assembly of Colloidal Nanocrystals through Regioselective Formation of Hydrogen-Bonded Supramolecular Bridges.

The linear assembly of nanocrystals (NCs) with orientational order presents a significant challenge in the field of colloidal assembly. This study presents an efficient strategy for assembling oleic acid (OAH)-capped, faceted rare earth NCs─such as nanorods, nanoplates, and nanodumbbells─into flexible chain-like superstructures. Remarkably, these NC chains exhibit a high degree of particle orientation even with an interparticle distance reaching up to 15 nm. Central to this oriented assembly method is the facet-selective adsorption of low-molecular-weight polyethylene glycol (PEG), such as PEG-400 (Mn = 400), onto specific facets of NCs. This regioselectivity is achieved by exploiting the lower binding affinity of OAH ligands on the (100) facets of rare earth NCs, enabling facet-specific ligand displacement and subsequent PEG attachment. By adjusting the solvent polarity, the linear assembly of NCs is induced by the solvophobic effect, which simultaneously promotes the formation of hydrogen-bonded PEG supramolecular bridges. These supramolecular bridges effectively connect NCs and exhibit sufficient robustness to maintain the structural integrity of the chains, despite the large interparticle spacing. Notably, even when coassembling different types of NCs, the resulting multicomponent chains still feature highly selective facet-to-facet connections. This work not only introduces a versatile method for fabricating well-aligned linear superstructures but also provides valuable insights into the fundamental principles governing the facet-selective assembly of NCs in solution.

Correction: Controllable synthesis of star-shaped FeCoMnOx nanocrystals and their self-assembly into superlattices with low-packing densities.

Correction for 'Controllable synthesis of star-shaped FeCoMnOx nanocrystals and their self-assembly into superlattices with low-packing densities' by Zhe Xia et al., Chem. Commun., 2024, 60, 3409-3412, https://doi.org/10.1039/D4CC00332B.

Encasing Few-Layer MoS2 within 2D Ordered Cubic Graphitic Cages to Smooth Trapping-Conversion of Lithium Polysulfides for Dendrite-Free Lithium-Sulfur Batteries.

The industrialization of lithium-sulfur (Li-S) batteries faces challenges due to the shuttling effect of lithium polysulfides (LiPSs) and the growth of lithium dendrites. To address these issues, a simple and scalable method is proposed to synthesize 2D membranes comprising a single layer of cubic graphitic cages encased with few-layer, curved MoS2. The distinctive 2D architecture is achieved by confining the epitaxial growth of MoS2 within the open cages of a 2D-ordered mesoporous graphitic framework (MGF), resulting in MoS2@MGF heterostructures with abundant sulfur vacancies. The experimental and theoretical studies establish that these MoS2@MGF membranes can act as a multifunctional interlayer in Li-S batteries to boost their comprehensive performance. The inclusion of the MoS2@MGF interlayer facilitates the trapping and conversion kinetics of LiPSs, preventing their shuttling effect, while simultaneously promoting uniform lithium deposition to inhibit dendrite growth. As a result, Li-S batteries with the MoS2@MGF interlayer exhibit high electrochemical performance even under high sulfur loading and lean electrolyte conditions. This work highlights the potential of designing advanced MoS2-encased heterostructures as interlayers, offering a viable solution to the current limitations plaguing Li-S batteries.

Controllable synthesis of star-shaped FeCoMnOx nanocrystals and their self-assembly into superlattices with low-packing densities.

We present a novel method for synthesizing monodisperse, star-shaped FeCoMnOx nanocrystals with tunable concavity. Through liquid-air interfacial assembly, these colloidal nanostars can form two-dimensional superlattices, which are characterized by low packing densities. Notably, the ability to adjust the degree of concavity of nanostars allows for the tuning of the packing symmetry of the assembled superlattices.

Macroscopic Superlattice Membranes Self-Assembled from Gold Nanobipyramids with Precisely Tunable Tip Arrangements for SERS.

A persistent challenge in utilizing Au nanocrystals for surface-enhanced Raman spectroscopy (SERS) lies in achieving controllable superstructures that maximize SERS performance. Here, a novel strategy is proposed to enhance the SERS performance by precisely adjusting the tip arrangements of Au nanobipyramids (BPs) in two-dimensional (2D) superlattices (SLs). This is achieved through ligand-exchange of Au BPs, followed by liquid-air interfacial assembly, resulting in large-area, transferrable SL membranes. The key to controlling the arrangement of Au BPs in the SLs is the regulation of the amount of free ligands added during self-assembly, which allows for the precise formation of various configurations such as tilted SLs, tip-on-tip SLs, and tip-to-tip SLs. Among these configurations, tip-on-tip SLs exhibit the highest enhancement factor for SERS, reaching an impressive value of 1.95×108, with uniform and consistent SERS signals across a large area. The experimental findings are further corroborated by simulations using the finite element method. This study establishes an efficient method for engineering the microstructure of 2D SLs composed of Au BPs, highlighting the importance of fine-tuning the tip arrangements of Au BPs to regulate SERS performance.

Molecularly Confined Topochemical Transformation of MXene Enables Ultrathin Amorphous Metal-Oxide Nanosheets.

Two-dimensional (2D) amorphous nanosheets with ultrathin thicknesses have properties that differ from their crystalline counterparts. However, conventional methods for growing 2D materials often produce either crystalline flakes or amorphous nanosheets with an uncontrollable thickness. Here, we report that ultrathin amorphous metal-oxide nanosheets featuring superior flatness can be realized through the molecularly confined topochemical transformation of MXene. Using MXene Ti2CTx as an example, we show that surface modification of Ti2CTx nanosheets with molecular ligands, such as oleylamine (OAm) and oleic acid (OA), not only imparts notable colloidal dispersity to Ti2CTx nanosheets in nonpolar organic solvents but also confines their subsequent oxidation to in-plane configurations. We demonstrate that unlike the drastic oxidation conventionally observed for pristine MXene, hydrophobizing MXene with OAm and OA ligands enables individual Ti2CTx nanosheets to undergo independent oxidation in a nondestructive manner, resulting in amorphous titanium oxide (am-TiO2) nanosheets that faithfully retain the dimension and flatness of pristine MXene. These am-TiO2 nanosheets exhibit exceptional activity as substrates for surface-enhanced Raman scattering. Importantly, this molecular confinement strategy can be extended to other MXene materials, providing a versatile approach for synthesizing ultrathin amorphous metal-oxide nanosheets with tailored compositions and functionalities.

Interfacial Assembly of Nanocrystals on Nanofibers with Strong Interaction for Electrocatalytic Nitrate Reduction.

One-dimensional fiber architecture serves as an excellent catalyst support. The orderly arrangement of active materials on such a fiber substrate can enhance catalytic performance by exposing more active sites and facilitating mass diffusion; however, this remains a challenge. We developed an interfacial assembly strategy for the orderly distribution of metal nanocrystals on different fiber substrates to optimize their electrocatalytic performance. Using electrochemical nitrate reduction reaction (NO3 - RR) as a representative reaction, the iron-based nanofibers (Fe/NFs) assembly structure achieved an excellent nitrate removal capacity of 2317 mg N/g Fe and N2 selectivity up to 97.2 %. This strategy could promote the rational design and synthesis of fiber-based electrocatalysts.

Monolayer supertubes of Carbon-Armored platinum nanocrystals enabling robust oxygen reduction electrocatalysis.

Self-assembled superstructures composed of nanocrystals (NCs) have shown immense potential for enhancing the performance in electrocatalytic applications. However, there has been limited research on the self-assembly of platinum (Pt) into low-dimensional superstructures as efficient electrocatalysts for oxygen reduction reaction (ORR). In this study, we designed a unique tubular superstructure composed of monolayer or sub-monolayer carbon-armored platinum nanocrystals (Pt NCs) using a template-assisted epitaxial assembly approach. The organic ligands on the surface of Pt NCs were in situ carbonized, resulting in few-layer graphitic carbon shells that encapsulate Pt NCs. Due to their monolayer assembly and tubular geometry, the Pt utilization of the supertubes was 1.5 times higher than that of conventional carbon-supported Pt NCs. As a result, such Pt supertubes exhibit remarkable electrocatalytic performance for the ORR in acidic media, with a high half-wave potential of 0.918 V and a high mass activity of 181 A g-1Pt at 0.9 V, which are comparable to commercial carbon-supported Pt (Pt/C) catalysts. Furthermore, the Pt supertubes demonstrate robust catalytic stability, as confirmed by long-term accelerated durability tests and identical-location transmission electron microscopy. This study presents a new approach to designing Pt superstructures for highly efficient and stable electrocatalysis.

An elegant 3D-ordered hierarchically porous framework to anchor Pt nanocrystals for durable oxygen reduction reaction.

While Platinum (Pt)-based electrocatalysts have been extensively studied for the oxygen reduction reaction (ORR), improving their durability remains a challenge. One promising approach is to design structure-defined carbon supports that can uniformly immobilize Pt nanocrystals (NCs). In this study, we present an innovative strategy for constructing three-dimensional ordered, hierarchically porous carbon polyhedrons (3D-OHPCs) as an efficient support for immobilizing Pt NCs. We achieved this by template-confined pyrolysis of a zinc-based zeolite imidazolate framework (ZIF-8) grown within the voids of polystyrene templates, followed by carbonizing the native oleylamine ligands on Pt NCs to produce graphitic carbon shells. This hierarchical structure enables the uniform anchorage of Pt NCs, while enhancing facile mass transfer and local accessibility of active sites. The optimal material with graphitic carbon armor shells on the surface of Pt NCs (CA-Pt), named CA-Pt@3D-OHPCs-1600, shows comparable activities to commercial Pt/C catalysts. Furthermore, it can withstand over 30,000 cycles of accelerated durability tests, owing to the protective carbon shells and hierarchically ordered porous carbon supports. Our study presents a promising approach for designing highly efficient and durable electrocatalysts for energy-based applications and beyond.

Shape-Mediated Oriented Assembly of Concave Nanoparticles under Cylindrical Confinement.

This contribution describes the self-assembly of colloidal nanodumbbells (NDs) with tunable shapes within cylindrical channels. We present that the intrinsic concave geometry of NDs endows them with peculiar packing and interlocking behaviors, which, in conjunction with the adjustable confinement constraint, leads to a variety of superstructures such as tilted-ladder chains and crossed-chain superlattices. A mechanistic investigation, corroborated by geometric calculations, reveals that the phase behavior of NDs under strong confinement can be rationalized by the entropy-driven maximization of the packing efficiency. Based on the experimental results, an empirical phase diagram is generated, which could provide general guidance in the design of intended superstructures from NDs. This study provides essential insight into how the interplay between the particle shape and confinement conditions can be exploited to direct the orientationally ordered assembly of concave nanoparticles into unusual superlattices.

Amphiphilic Self-Assembly of Nanocrystals at Emulsion Interface Renders Fast and Scalable Quasi-Nanosheet Formation.

Scalable assembly of nanocrystals (NCs) into two-dimensional (2D) nanosheets has aroused great interest, yet it remains under-explored. This is because current 2D assembly methods rely mainly on the use of solid- or liquid-air interfaces, which are inherently difficult for upscaling and thus lack practicability. Here, with a microemulsion-based amphiphilic assembly technique, we achieve a fast and scalable preparation of free-standing nanosheets comprising few-layer, tightly packed NCs, namely, quasi-nanosheets (quasi-NSs). Acetic acid, acting as both solvent and surface-treatment agent, is used to render the initially hydrophobic NCs amphiphilic, while simultaneously inducing the interfacial instability right after the assembly of NCs at the emulsion interface to afford quasi-NSs. This amphiphilic assembly method is applicable to a variety of NCs, and multicomponent quasi-NSs are also attainable upon coassembly of different types of NCs. In addition, the structural advantages of quasi-NSs in catalysis are showcased by using NiFe2O4 quasi-NSs as electrocatalysts for the oxygen evolution reaction. This work opens a new route for the scalable construction of 2D NC sheets with designated components and functions.

Mismatched ligand density enables ordered assembly of mixed-dimensional, cross-species materials.

The ordered coassembly of mixed-dimensional species-such as zero-dimensional (0D) nanocrystals and 2D microscale nanosheets-is commonly deemed impracticable, as phase separation almost invariably occurs. Here, by manipulating the ligand grafting density, we achieve ordered coassembly of 0D nanocrystals and 2D nanosheets under standard solvent evaporation conditions, resulting in macroscopic, freestanding hybrid-dimensional superlattices with both out-of-plane and in-plane order. The key to suppressing the notorious phase separation lies in hydrophobizing nanosheets with molecular ligands identical to those of nanocrystals but having substantially lower grafting density. The mismatched ligand density endows the two mixed-dimensional components with a molecular recognition-like capability, driving the spontaneous organization of densely capped nanocrystals at the interlayers of sparsely grafted nanosheets. Theoretical calculations reveal that the intercalation of nanocrystals can substantially reduce the short-range repulsions of ligand-grafted nanosheets and is therefore energetically favorable, while subsequent ligand-ligand van der Waals attractions induce the in-plane order and kinetically stabilize the laminate superlattice structure.

Synthesis of silica-stabilized Ag44 clusters aided by a designed mercaptosilane ligand.

The novel and precise design of both a microscopic ligand and macroscopic structure has been demonstrated to improve the stability and potential optical applications of Ag44 clusters. The ligand with designed silane substituents on its thiophenol enabled the synthesized [Ag44(SPhSi(OEt)3)30](PPh4)4 clusters to maintain UV-vis absorption for 13 h when heated at 60 °C in air and be readily coated with silica shells via a one-pot reverse microemulsion method. This composite structure overcomes the issue that non-luminescent Ag44 clusters cannot be applied in photothermal and photoacoustic imaging due to their instability.

Modular super-assembly of hierarchical superstructures from monomicelle building blocks.

Manipulating the super-assembly of polymeric building blocks still remains a great challenge due to their thermodynamic instability. Here, we report on a type of three-dimensional hierarchical core-satellite SiO2@monomicelle spherical superstructures via a previously unexplored monomicelle interfacial super-assembly route. Notably, in this superstructure, an ultrathin single layer of monomicelle subunits (~18 nm) appears in a typically hexagon-like regular discontinuous distribution (adjacent micelle distance of ~30 nm) on solid spherical interfaces (SiO2), which is difficult to achieve by conventional super-assembled methods. Besides, the number of the monomicelles on colloidal SiO2 interfaces can be quantitatively controlled (from 76 to 180). This quantitative control can be precisely manipulated by tuning the interparticle electrostatic interactions (the intermicellar electrostatic repulsion and electrostatic attractions between the monomicelle units and the SiO2 substrate). This monomicelle interfacial super-assembly strategy will enable a controllable way for building multiscale hierarchical regular micro- and/or macroscale materials and devices.

Native Ligand Carbonization Renders Common Platinum Nanoparticles Highly Durable for Electrocatalytic Oxygen Reduction: Annealing Temperature Matters.

Current protocols for synthesizing monodisperse platinum (Pt) nanoparticles typically involve the use of hydrocarbon molecules as surface-capping ligands. Using Pt nanoparticles as catalysts for the oxygen reduction reaction (ORR), however, these ligands must be removed to expose surface sites. Here, highly durable ORR catalysts are realized without ligand removal; instead, the native ligands are converted into ultrathin, conformal graphitic shells by simple thermal annealing. Strikingly, the annealing temperature is a critical factor dictating the ORR performance of Pt catalysts. Pt nanoparticles treated at 500 °C show a very poor ORR activity, whereas those annealed at 700 °C become highly active along with exceptional stability. In-depth characterization reveals that thermal treatment from 500 to 700 °C gradually opens up the porosity in carbon shells through graphitization. Importantly, such graphitic-shell-coated Pt catalysts exhibit a superior ORR stability, largely retaining the activity after 20 000 cycles in a membrane electrode assembly. Moreover, this ligand carbonization strategy can be extended to modify commercial Pt/C catalysts with substantially enhanced stability. This work demonstrates the feasibility of boosting the ORR performance of common Pt nanoparticles by harnessing the native surface ligands, offering a robust approach of designing highly durable catalysts for proton-exchange-membrane fuel cells.

Hard-templated engineering of versatile 2D amorphous metal oxide nanosheets.

Two-dimensional (2D) nanomaterials have received ever-increasing attention and in-depth exploration in multifarious fields on account of their superior mass transfer ability and abundant catalytic-active sites. Especially, the amorphous 2D nanomaterials feature unique properties distinct from atomic crystalline materials. However, the synthesis of high-quality and large-sized amorphous 2D nanomaterials encounters a big challenge. Here, a general and facile synthetic strategy for a series of 2D amorphous metal and nonmetallic oxides nanosheets, including SiO2, AlOOH, ZrO2and TiO2nanosheets, is reported. The versatile 2D amorphous nanomaterials are fabricatedviamanipulating the surface energy of relevant metal alkoxide precursors with liquid feature and controlling the related synthesis parameters to form solid 2D amorphous nanosheets byin situhydrolysis and condensation of precursors. Density functional theory (DFT) calculations reveal the molecular adsorption mechanism of wetting process of precursor infiltrated on solid NaCl substrate, which attributes to the strong interaction between Na-O atom pairs from NaCl and metal alkoxides respectively. Furthermore, taking the 2D Fe-ZrO2nanomaterials as the catalyst, the excellent catalytic performance for Rhodamine B (RhB) degradation illustrates that these 2D nanomaterials prepared by this method have the characteristics of easy functionalization. This work provides an efficient strategy for nanomaterials functionalization during 2D nanosheets synthetic process and further being applied in catalysis-related field and beyond.

Gelation-Assisted Assembly of Large-Area, Highly Aligned, and Environmentally Stable MXene Films with an Excellent Trade-Off between Mechanical and Electrical Properties.

Layered MXene films have shown enormous potential for wide applications due to their high electrical conductivity and unique laminated microstructure. However, the intrinsic susceptibility to oxidation and the mechanical fragility of MXene films are the two major bottlenecks that prevent their widespread industrial applications. Here, a facile yet efficient assembly strategy is proposed to address these issues by increasing the alignment and compactness of MXene layers as well as strengthening the interlayer interactions. This method involves the gelation of MXene flakes with a multifunctional inorganic "mortar" polymer (ammonium polyphosphate, APP) followed by quasi-solid-state assembly enabled by a mechanical rolling process, by which the 3D gel network is transformed into 2D freestanding MXene films with unprecedented flake alignment and compactness. Besides, due to the multiple molecular-level interactions (hydrogen bonding, coordination bonding, and electrostatic force) between APP and MXene flakes, the resultant MXene-APP film (MAF) displays high mechanical strength (286.4 ± 20.3 MPa) and excellent electrical conductivity (8012.4 ± 325.6 S cm-1 ), along with remarkable environmental stability. As an application demonstration, MAF exhibits outstanding electromagnetic interference shielding effectiveness with long-term durability, highlighting the great potential of this gelation-assisted assembly strategy in fabricating large-area, high-performance MXene films for diverse real-world applications.

A universal, green, and self-reliant electrolytic approach to high-entropy layered (oxy)hydroxide nanosheets for efficient electrocatalytic water oxidation.

The development and exploration of high-entropy materials with tunable chemical compositions and unique structural characteristics, although challenging, have attracted increasingly greater attention over the past few years. Here, we report a universal and green method to prepare high-entropy layered (oxy)hydroxide (HE-LH) nanosheets under ambient conditions. This method is based on a self-reliant electrochemical process, utilizing only low-cost metal foils and electrolytes as reactant, with no need of involving extra alkali salts and/or organic reagents. Importantly, the composition of HE-LH nanosheets is widely tunable by simply adjusting the combination of metal foils. As a representative example, quinary layered (oxy)hydroxide (CoFeNiCrV-LH) nanosheets are rationally designed, which exhibit superior electrocatalytic activity and long-term durability towards the electrocatalytic oxygen evolution reaction, outperforming both CoFe layered double hydroxides and most previously reported transition-metal-based electrocatalysts. Comprehensive characterization and analysis reveal that the high-entropy effects play a significant role in forming the defect-rich, low-crystalline microstructures, along with large specific surface areas and optimized electronic configurations, thus enabling the boosted electrocatalytic performance. This electrochemical synthetic approach is generally applicable to the scalable synthesis of diverse HE-LH materials towards versatile promising applications.

Confinement Assembly in Polymeric Micelles Enables Nanoparticle Superstructures with Tunable Molecular-Like Geometries.

The self-assembly of a small number of nanoparticles into superstructures that mimic the geometry of molecules provides an unprecedented route for creating materials with precisely defined structures and potentially programmable functionalities. Such nanoparticle clusters (NPCs), also known as colloidal molecules, have a wide range of applications due to the decisive ensemble effect. Here, a universal and straightforward strategy is developed to construct NPCs with tunable molecular-like geometries by confining the self-assembly of hydrophobic nanoparticles within micelles formed by amphiphilic copolymers. It is found that confinement assembly of both spherical and anisotropic nanoparticles can lead to NPCs, the molecular-like conformation of which is widely tunable by adjusting the ratio between copolymers and nanoparticles. Mechanistic studies reveal the formation of large-vesicle intermediates along the path toward forming NPCs. This work establishes a facile and general strategy of assembling finite nanoparticles with precisely tunable geometries without introducing any directional interactions, which can accelerate the exploration of clustered superstructures toward broad applications.