Kun Wang

Ru-CoNiS _x /NF catslyst delivers excellent SOR-coupled HER performance. Replacing OER with sulfur oxidation enables energy-saving H ₂ production while promoting sulfur recovery.

The V-doped MoO _x subnanoclusters (∼0.7 nm) anchored on carboxylated CNTs modulate the MoO _x electronic structure, delivering 98% H ₂ O ₂ selectivity at 0.4 V with minimal decay over 10 h.

The ultimate miniaturization of catalysts to single-atomic dimensions offers a promising route to maximize the catalytic performance through fully exposed active sites and precisely tailored electronic structures. However, the synthesis of atomically precise one-dimensional single-cluster or single-atom catalysts with the simplest periodicity remains challenging due to their thermodynamic instability. Here, we report a general strategy for fabricating single-unit-chain catalysts confined within single-walled carbon nanotubes (SWCNTs), where charge delocalization dramatically enhances the catalytic performance. Through a liquid-phase assembly approach, diverse clusters and atoms can be uniformly packed into ordered single-unit chains inside SWCNTs, irrespective of their electronic properties or solubility. These identical, well-defined single-unit chains maintain intimate contact with the conductive graphene walls of SWCNTs, enabling tunable positive or negative charge delocalization across the nanotube surfaces. The resulting catalysts demonstrate remarkable activity enhancements in both redox and coupling reactions, exhibiting rate constants 7.5∼28 times greater than their isolated cluster counterparts. Mechanistic studies reveal that charge delocalization simultaneously increases the density of active sites and reduces the activation barriers. This synthetic approach and catalytic mechanism show universal applicability to various single-chain catalysts. These systems maintain nearly undiminished activity in 230 h continuous-flow reactions, highlighting their exceptional stability for practical applications.

Thin-film β tungsten (β-W), a metastable phase of tungsten, holds significant potential in the fabrication of superconducting and spin-memory devices. However, due to the rapid surface passivation of tungsten in oxygen and moisture, the synthesis of nanosized metastable β-W with the intrinsic atomic surface is still difficult, and their magnetic properties remain rather unexplored. Inspired by the strong host-guest interaction-induced stabilization, we reported the synthesis of atomically thin (1.0-1.3 nm) metastable β-W nanowires within single-walled carbon nanotubes (SWCNTs) through an oxygen-assisted transformation of starting W₂C, with 85% of β-W nanowires along the anisotropic ⟨010⟩ direction. Atomically resolved electron microscopy directly unveils the dynamic evolutions of W₂C-to-β-W and further β-to-α-W within SWCNTs, depending on the H₂-annealing time. Detailed mechanistic studies by theoretical calculations and experiments reveal that oxygen diffused within the W₂C lattice governs the formation and stabilization of ultrathin β-W nanowires within the SWCNTs. Additionally, the nanoconfinement of SWCNTs, restricting the thickness of W nanowires down to 2 nm, also benefits the thermodynamically favorable nucleation of β-W than α-W. With the protection of a single graphene layer against water erosion, β-W@SWCNTs exhibit a ferromagnetic response at ∼130 K, with higher chemical stability than fully exposed thin-film β-W. This work may provide a feasible way to design the ferromagnetic nanowire metamaterials based on aligned SWCNT arrays that have the potential to fabricate microwave and spin devices.

Insight into the behaviors of molecules in confined space is highly desired for the deep understanding of the mechanism of chemical reactions in a microenvironment. Yet the direct access of molecular evolutions at atomic resolution in nanoconfinements is still challenging. Among various guests, atomically precise clusters with well-defined structures are better suited for monitoring the chemical and physical processes in nanochannels because of their visibility under electron microscopy and identical structures that ensure homogeneous interactions. Developing an efficient method for assembling clusters into a confined space is essential for advancing mechanisms of these processes. In this Perspective, we provide an overview of the assembly of clusters into single-walled carbon nanotubes (SWCNTs) in the liquid phase. We begin with the introduction of assembling methodologies, followed by a discussion of mechanisms of confined assembly in liquids. The host-guest interactions between clusters and nanotubes and the molecular reactions in nanochannels revealed by transmission electron microscopy are unveiled, and the cluster@SWCNT heterostructure-based emerging applications are highlighted. At the end, we discuss the challenges and opportunities and expound our outlook in this field.

We realized the confined assembly of uranyl within single-walled carbon nanotubes and unveiled the directional growth and reconstruction of U₄O₉ nanorods in nanochannels enabled by in situ transmission electron microscopy e-beam stimulation.

High-entropy intermetallic (HEI) nanocrystals, composed of multiple elements with an ordered structure, are of immense interest in heterogeneous catalysis due to their unique geometric and electronic structures and the cocktail effect. Despite tremendous efforts dedicated to regulating the metal composition and structures with advanced synthetic methodologies to improve the performance, the surface structure, and local chemical order of HEI and their correlation with activity at the atomic level remain obscure yet challenging. Herein, by determining the three-dimensional (3D) atomic structure of quinary PdFeCoNiCu (PdM) HEI using atomic-resolution electron tomography, we reveal that the local chemical order of HEI regulates the surface electronic structures, which further mediates the alkyl-substitution-dependent alkyne semihydrogenation. The 3D structures of HEI PdM nanocrystals feature an ordered (intermetallic) core enclosed by a disordered (solid-solution) shell rather than an ordered surface. The lattice mismatch between the core and shell results in apparent near-surface distortion. The chemical order of the intermetallic core increases with annealing temperature, driving the electron redistribution between Pd and M at the surface, but the surface geometrical (chemically disordered) configurations and compositions are essentially unchanged. We investigate the catalytic performance of HEI PdM with different local chemical orders toward semihydrogenation across a broad range of alkynes, finding that the electron density of surface Pd and the hindrance effect of alkyl substitutions on alkynes are two key factors regulating selective semihydrogenation. We anticipate that these findings on surface atomic structure will clarify the controversy regarding the geometric and/or electronic effects of HEI catalysts and inspire future studies on tuning local chemical order and surface engineering toward enhanced catalysts.

Single-walled carbon nanotube (SWCNT) heterostructures have shown great potential in catalysis, magnetism, and nanofluidics, in which host SWCNTs with certain conductivity (metallic or semiconducting) are highly required. Herein, inspired by the large molecular weight and redox properties of polyoxometalate (POM) clusters, we reported the selective separation of POM encapsulated metallic SWCNTs (POM@m-SWCNTs) with a uniform diameter through density gradient ultracentrifugation (DGU). The confined POMs increased the SWCNT density and amplified the nanotubes' density difference, thus greatly lowering the centrifugal force (70,000g) of DGU. With this strategy, a series of POM@m-SWCNTs of ∼1.2 nm with high purity were sorted. The mechanism supported by theoretical and experimental evidence showed that the separation of m-SWCNTs depended on not only nanotube/cluster size but also the conductivity of SWCNTs. The smallest 1.2 nm m-SWCNT that can exactly accommodate a 0.9 nm-{Mo₆} cluster exhibited the maximum electron transfer to inner clusters; thus, intertube π-π stacking of such m-SWCNTs was greatly loosened, leading to the preferential dispersion into individual ones and partitioning in the uppermost layer after DGU. As a proof-of-concept application, this sorting strategy was extended to separate heavy-element ²³⁸U-encapsulated m-SWCNTs. The phase-pure, tiny (1-2.5 nm) U₄O₉ crystals with atomic vacancy clusters were fabricated on m-SWCNTs through growth kinetic control. This work may provide a general way to construct desired actinide materials on specific SWCNTs.