Boosting Bifunctional Catalysis by Integrating Active Faceted Intermetallic Nanocrystals and Strained Pt-Ir Functional Shells.

PtIr-based nanostructures are fascinating materials for application in bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysis. However, the fabrication of PtIr nanocatalysts with clear geometric features and structural configurations, which are crucial for enhancing the bifunctionality, remains challenging. Herein, PtCo@PtIr nanoparticles are precisely designed and fabricated with a quasi-octahedral PtCo nanocrystal as a highly atomically ordered core and an ultrathin PtIr atomic layer as a compressively strained shell. Owing to their geometric and core-shell features, the PtCo@PtIr nanoparticles deliver approximately six and eight times higher mass and specific activities, respectively, as an ORR catalyst than a commercial Pt/C catalyst. The half-wave potential of PtCo@PtIr exhibits a negligible decrease by 9 mV after 10 000 cycles, indicating extraordinary ORR durability because of the ordered arrangement of Pt and Co atoms. When evaluated using the ORR-OER dual reaction upon the introduction of Ir, PtCo@PtIr exhibits a small ORR-OER overpotential gap of 679 mV, demonstrating its great potential as a bifunctional electrocatalyst for fabricating fuel cells. The findings pave the way for designing precise intermetallic core-shell nanocrystals as highly functional catalysts.

Niobium Oxide Anode with Lattice Structure Self-Optimization for High-Power and Nearly Zero-Degeneration Battery Operation.

Li+ insertion-induced structure transformation in crystalline electrodes vitally influence the energy density and cycle life of secondary lithium-ion battery. However, the influence mechanism of structure transformation-induced Li+ migration on the electrochemical performance of micro-crystal materials is still unclear and the strategy to profit from such structure transformation remains exploited. Here, an interesting self-optimization of structure evolution during electrochemical cycling in Nb2 O5 micro-crystal with rich domain boundaries is demonstrated, which greatly improves the charge transfer property and mechanical strength. The lattice rearrangement activates the Li+ diffusion kinetics and hinders the particle crack, thus enabling a nearly zero-degeneration operation after 8000 cycles. Full cell paired with lithium cobalt oxides displays an exceptionally high capacity of 176 mA h g-1 at 8000 mA g-1 and excellent long-term durability at 6000 mA g-1 with 63% capacity retention over 2000 cycles. Interestingly, a unique fingerprint based on the intensity ratio of two X-ray diffraction peaks is successfully extracted as a measure of Nb2 O5 electrochemical performance. The structure self-optimization for fast charge transfer and high mechanical strength exemplifies a new battery electrode design concept and opens up a vast space of strategy to develop high-performance lithium-ion batteries with high energy density and ultra-long cycle life.

Controlled Growth of Pd Nanocrystals by Interface Interaction on Monolayer MoS2: An Atom-Resolved in Situ Study.

The crystal growth kinetics is crucial for the controllable preparation and performance modulation of metal nanocrystals (NCs). However, the study of growth mechanisms is significantly limited by characterization techniques, and it is still challenging to in situ capture the growth process. Real-time and real-space imaging techniques at the atomic scale can promote the understanding of microdynamics for NC growth. Herein, the growth of Pd NCs on monolayer MoS2 under different atmospheres was in situ studied by environmental transmission electron microscopy. Introducing carbon monoxide can modulate the diffusion of Pd monomers, resulting in the epitaxial growth of Pd NCs with a uniform orientation. The electron energy loss spectroscopy and theoretical calculations showed that the CO adsorption assured the specific exposed facets and good uniformity of Pd NCs. The insight into the gas-solid interface interaction and the microscopic growth mechanism of NCs may shed light on the precise synthesis of NCs on two-dimensional (2D) materials.

Unraveling the Atomic Shuffles of Twinning Nucleation in Hexagonal Close-Packed Rhenium Nanocrystals.

Reining in deformation twinning is crucial for the mechanical properties of hexagonal close-packed (HCP) metals and hinges on an explicit understanding of the twinning nucleation mechanism. Unfortunately, it is often suggested rather than conclusively demonstrated that twinning nucleation can be mediated by pure atomic shuffles. Herein, by utilizing in situ high-resolution transmission electron microscopy, we have dissected the atomic shuffling mechanism during the {101̅2} twinning nucleation in rhenium nanocrystals, which revealed the emergence of an intermediate body-centered tetragonal (BCT) structure. Specifically, the double-layered prismatic planes initially shuffle into single-layered {11̅0}BCT planes; subsequently, adjacent {22̅0}BCT planes shuffle in opposite directions to form the basal planes of the twin embryo. This shuffling mechanism is further corroborated by molecular dynamic simulations. The finding provides direct evidence of shuffle-dominated twinning nucleation with atomic details that may lead to better control of this critical twinning mode in HCP metals.

An Ultrastable Bifunctional Electrocatalyst Derived from a Co2+-Anchored Covalent-Organic Framework for High-Efficiency ORR/OER and Rechargeable Zinc-Air Battery.

It remains a great challenge to develop alternative electrocatalysts with high stability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a bifunctional electrocatalyst composed of hollow CoOx (Co3O4/CoO) nanoparticles embedded in lamellar carbon nanofibers is derived from a Co2+-anchored covalent-organic framework. The as-fabricated electrocatalyst (CoOx@NC-800) exhibits a half-wave potential (E1/2) of 0.89 V with ultrahigh long-term stability (100% current retention after 3000 CV cycles). Together with promising OER performance, the CoOx@NC-800 based reversible Zn-air battery displays a small potential gap (0.70 V), superior to that of the commercial 20% Pt/C + RuO2. The density functional theory (DFT) calculations reveal that the remarkable electrocatalytic performance and stability of CoOx@NC-800 are attributed to the optimized adsorption of the *OOH intermediate and reduced free energy of the potential-limiting step. This study establishes the functionalization of COF structure for fabrication of high-performance carbon-based electrocatalysts.

Nucleation and Growth of Nanocrystals Investigated by In Situ Transmission Electron Microscopy.

Nanocrystals play a key role in the modern energy, catalysis, semiconductor, and biology industries due to their unique structures and performances. However, controllable fabrication of ideal nanocrystals with the desired structures and properties is still challenging, which needs a deep understanding of their nucleation and growth process. Here, the research on nucleation and growth of nanocrystals studied by in situ transmission electron microscopy (TEM) is reviewed, mainly focusing on the atomic migration dynamics, interface evolution, and structure transformation. In addition, the challenges in the study of nanocrystal growth by TEM are discussed and the perspective on the future development of advanced in situ TEM techniques is provided. It is hoped that the review can give a deep insight into the nanocrystal nucleation and growth process, and further contribute to the rational design and precise fabrication of high-performance functional nanocrystals.

Correlation Between Serum ESPL1 and Hepatitis B Virus-related Hepatocellular Carcinoma Histological Grade: A Chinese Single-center Case-control Study.

BACKGROUND/AIM: Serum markers to determine the histological grade of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) are still limited. This study aimed to investigate if serum extra spindle pole bodies-like 1 (ESPL1) protein could reflect the histological grade of HBV-related HCC. MATERIALS AND METHODS: A total of 154 patients with HBV-related HCC were enrolled in the experimental group and 41 non-HBV-related patients in the control. Enzyme-linked immunosorbent assay was used to detect serum ESPL1 levels. The differences in serological ESPL1, alpha-fetoprotein (AFP), and des-gamma-carboxy prothrombin (DCP) were compared between the two groups. HCC tumor diameter was measured, and pathological examination was performed to compare the relationship between ESPL1, AFP, and DCP and tumor size and histological grade. RESULTS: Serum AFP and DCP levels showed no significant difference between experimental group and control group, and increased when the tumor diameter increased but were not related to HCC histological grade. Serological ESPL1 levels were higher in the experimental group than those in the control group, and positively correlated with the histological grade. In the experimental group, tumor size and histological grade were almost independent (Kappa=0.000); patients with medium size tumors had the highest serum ESPL1 levels and the highest proportion of poorly differentiated carcinomas, whereas 75.6% of patients with small size tumors had moderately differentiated carcinomas and only 20% well differentiated carcinomas. CONCLUSION: Serum ESPL1 can reflect the malignant degree of HBV-related HCC and is helpful in identifying small size HCC tumors.

Growth of few-layer WTe2 by a salt-assisted double-tube chemical vapor deposition method with high infrared photosensitivity.

WTe2, as a member of Weyl semimetals, is a vital candidate for the development of broad-wavelength-range photodetectors. At present, the preparation of WTe2 films mainly depends on the chemical vapor deposition (CVD) method. However, the chemical reactivity between W and Te is low, and the controllable synthesis of large-sized layered WTe2 in a stoichiometric ratio is the main challenge for further research. Here, we propose a salt-assisted double-tube CVD method for the one-step preparation of high-quality and large-size WTe2 crystals with a monolayer and few layers. The thickness and lateral dimension of WTe2 crystals can be effectively tuned by the growth temperature and hydrogen concentration, and the dynamic growth mechanism is understood by the combination of surface reaction and mass transport. Furthermore, a high-performance photodetector based on WTe2 is fabricated, which has high responsivity of 118 mA W-1 (1550 nm) and 408 mA W-1 (2700 nm) at room temperature, indicating its great potential for application in infrared optoelectronic devices. The results provide a reference for the preparation of 2D materials by CVD and lay the foundation for the fabrication of next-generation optoelectronic devices with a wide-wavelength-range response.

Optimization Methods of Tungsten Oxide-Based Nanostructures as Electrocatalysts for Water Splitting.

Electrocatalytic water splitting, as a sustainable, pollution-free and convenient method of hydrogen production, has attracted the attention of researchers. However, due to the high reaction barrier and slow four-electron transfer process, it is necessary to develop and design efficient electrocatalysts to promote electron transfer and improve reaction kinetics. Tungsten oxide-based nanomaterials have received extensive attention due to their great potential in energy-related and environmental catalysis. To maximize the catalytic efficiency of catalysts in practical applications, it is essential to further understand the structure-property relationship of tungsten oxide-based nanomaterials by controlling the surface/interface structure. In this review, recent methods to enhance the catalytic activities of tungsten oxide-based nanomaterials are reviewed, which are classified into four strategies: morphology regulation, phase control, defect engineering, and heterostructure construction. The structure-property relationship of tungsten oxide-based nanomaterials affected by various strategies is discussed with examples. Finally, the development prospects and challenges in tungsten oxide-based nanomaterials are discussed in the conclusion. We believe that this review provides guidance for researchers to develop more promising electrocatalysts for water splitting.

Construction of the Heterostructure of NiPt Truncated Octahedral Nanoparticle/MoS2 and Its Interfacial Structure Evolution.

Interfacial atomic configuration plays a vital role in the structural stability and functionality of nanocomposites composed of metal nanoparticles (NPs) and two-dimensional semiconductors. In situ transmission electron microscope (TEM) provides a real-time technique to observe the interface structure at atomic resolution. Herein, we loaded bimetallic NiPt truncated octahedral NPs (TONPs) on MoS2 nanosheets and constructed a NiPt TONPs/MoS2 heterostructure. The interfacial structure evolution of NiPt TONPs on MoS2 was in situ investigated using aberration-corrected TEM. It was observed that some NiPt TONPs exhibited lattice matching with MoS2 and displayed remarkable stability under electron beam irradiation. Intriguingly, the rotation of an individual NiPt TONP can be triggered by the electron beam to match the MoS2 lattice underneath. Furthermore, the coalescence kinetics of NiPt TONPs can be quantitatively described by the relationship between neck radius (r) and time (t), expressed as rn = Kt. Our work offers a detailed analysis of the lattice alignment relationship of NiPt TONPs on MoS2, which may enlighten the design and preparation of stable bimetallic metal NPs/MoS2 heterostructures.

General Approach for Two-Dimensional Rare-Earth Oxyhalides with High Gate Dielectric Performance.

Two-dimensional (2D) rare-earth oxyhalides (REOXs) with novel properties offer fascinating opportunities for fundamental research and applications. The preparation of 2D REOX nanoflakes and heterostructures is crucial for revealing their intrinsic properties and realizing high-performance devices. However, it is still a great challenge to fabricate 2D REOX using a general approach. Herein, we design a facile strategy to prepare 2D LnOCl (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) nanoflakes using the molten salt method assisted by the substrate. A dual-driving mechanism was proposed in which the lateral growth could be guaranteed by the quasi-layered structure of LnOCl and the interaction between the nanoflakes and the substrate. Furthermore, this strategy has also been successfully applied for block-by-block epitaxial growth of diverse lateral heterostructures and superlattice. More significantly, the high performance of MoS2 field-effect transistors with LaOCl nanoflake as the gate dielectric was demonstrated, exhibiting competitive device characteristics of high on/off ratios up to 107 and low subthreshold swings down to 77.1 mV dec-1. This work offers a deep understanding of the growth of 2D REOX and heterostructures, shedding new light on the potential applications in future electronic devices.

Ortho Effects of Tricarboxylate Linkers in Regulating Topologies of Rare-Earth Metal-Organic Frameworks.

A linker design strategy is developed to attain novel polynuclear rare-earth (RE) metal-organic frameworks (MOFs) with unprecedented topologies. We uncover the critical role of ortho-functionalized tricarboxylate ligands in directing the construction of highly connected RE MOFs. The acidity and conformation of the tricarboxylate linkers were altered by substituting with diverse functional groups at the ortho position of the carboxyl groups. For instance, the acidity difference between carboxylate moieties resulted in forming three hexanuclear RE MOFs with novel (3,3,3,10,10)-c wxl, (3,12)-c gmx, and (3,3,3,12)-c joe topologies, respectively. In addition, when a bulky methyl group was introduced, the incompatibility between the net topology and ligand conformation guided the co-appearance of hexanuclear and tetranuclear clusters, generating a novel 3-periodic MOF with a (3,3,8,10)-c kyw net. Interestingly, a fluoro-functionalized linker prompted the formation of two unusual trinuclear clusters and produced a MOF with a fascinating (3,8,10)-c lfg topology, which could be gradually replaced by a more stable tetranuclear MOF with a new (3,12)-c lee topology with extended reaction time. This work enriches the polynuclear clusters library of RE MOFs and unveils new opportunities to construct MOFs with unprecedented structural complexity and vast application potential.

MoS2/NiSe2/rGO Multiple-Interfaced Sandwich-like Nanostructures as Efficient Electrocatalysts for Overall Water Splitting.

Constructing a heterogeneous interface using different components is one of the effective measures to achieve the bifunctionality of nanocatalysts, while synergistic interactions between multiple interfaces can further optimize the performance of single-interface nanocatalysts. The non-precious metal nanocatalysts MoS2/NiSe2/reduced graphene oxide (rGO) bilayer sandwich-like nanostructure with multiple well-defined interfaces is prepared by a simple hydrothermal method. MoS2 and rGO are layered nanostructures with clear boundaries, and the NiSe2 nanoparticles with uniform size are sandwiched between both layered nanostructures. This multiple-interfaced sandwich-like nanostructure is prominent in catalytic water splitting with low overpotential for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and almost no degradation in performance after a 20 h long-term reaction. In order to simulate the actual overall water splitting process, the prepared nanostructures are assembled into MoS2/NiSe2/rGO||MoS2/NiSe2/rGO modified two-electrode system, whose overpotential is only 1.52 mV, even exceeded that of noble metal nanocatalyst (Pt/C||RuO2~1.63 mV). This work provides a feasible idea for constructing multi-interface bifunctional electrocatalysts using nanoparticle-doped bilayer-like nanostructures.

Directional Migration and Rapid Coalescence of Au Nanoparticles on Anisotropic ReS2.

Interfacial atomic configuration and its evolution play critical roles in the structural stability and functionality of mixed zero-dimensional (0D) metal nanoparticles (NPs) and two-dimensional (2D) semiconductors. In situ observation of the interface evolution at atomic resolution is a vital method. Herein, the directional migration and structural evolution of Au NPs on anisotropic ReS2 were investigated in situ by aberration-corrected transmission electron microscopy. Statistically, the migration of Au NPs with diameters below 3 nm on ReS2 takes priority with greater probability along the b-axis direction. Density functional theory calculations suggest that the lower diffusion energy barrier enables the directional migration. The coalescence kinetics of Au NPs is quantitatively described by the relation of neck radius (r) and time (t), expressed as r2=Kt. Our work provides an atomic-resolved dynamic analysis method to study the interfacial structural evolution of metal/2D materials, which is essential to the study of the stability of nanodevices based on mixed-dimensional nanomaterials.

Mixed-Dimensional Pt-Ni Alloy Polyhedral Nanochains as Bifunctional Electrocatalysts for Direct Methanol Fuel Cells.

Pt nanocatalysts play a critical role in direct methanol fuel cells (DMFCs) due to their appropriate adsorption/desorption energy, yet suffer from an unbalanced relationship between size-dependent activity and stability. Herein, mixed-dimensional Pt-Ni alloy polyhedral nanochains (Pt-Ni PNCs) with an ordered assembly of a nanopolyhedra-nanowire-nanopolyhedra architecture are fabricated as bifunctional electrocatalysts for DMFCs, effectively alleviating the size effect. The Pt-Ni PNCs exhibit 7.23 times higher mass activity for the anodic methanol oxidation reaction (MOR) than that of commercial Pt/C. In situ Fourier transform infrared spectroscopy and CO stripping measurements demonstrate the prominent stability of the Pt-Ni PNCs to resist CO poisoning. For the cathodic oxygen reduction reaction (ORR), a positive half-wave potential exceeding Pt/C is achieved by the Pt-Ni PNCs, and it can be well maintained for 10 000 cycles with negligible activity decay. The designed nanostructure can alleviate the agglomeration and dissolution problems of 0D small-sized Pt-Ni alloy nanocrystals and enrich surface atom steps and active facets of 1D chain-like nanostructures. This work provides a proposed strategy to improve the catalytic performance of Pt-based nanocatalysts by constructing novel interfacial relationships in mixed dimensions to alleviate the imbalance between catalytic activity and catalytic stability caused by size effects.

Atomic-Scale Structure Dynamics of Nanocrystals Revealed By In Situ and Environmental Transmission Electron Microscopy.

Nanocrystals are of great importance in material sciences and industry. Engineering nanocrystals with desired structures and properties is no doubt one of the most important challenges in the field, which requires deep insight into atomic-scale dynamics of nanocrystals during the process. The rapid developments of in situ transmission electron microscopy (TEM), especially environmental TEM, reveal insights into nanocrystals to digest. According to the considerable progress based on in situ electron microscopy, a comprehensive review on nanocrystal dynamics from three aspects: nucleation and growth, structure evolution, and dynamics in reaction conditions are given. In the nucleation and growth part, existing nucleation theories and growth pathways are organized based on liquid and gas-solid phases. In the structure evolution part, the focus is on in-depth mechanistic understanding of the evolution, including defects, phase, and disorder/order transitions. In the part of dynamics in reaction conditions, solid-solid and gas-solid interfaces of nanocrystals in atmosphere are discussed and the structure-property relationship is correlated. Even though impressive progress is made, additional efforts are required to develop the integrated and operando TEM methodologies for unveiling nanocrystal dynamics with high spatial, energy, and temporal resolutions.

Rare-earth squarate frameworks with scu topology.

As a typical planar 4-connected ligand that possesses D4h symmetry, the squarate ligand is expected to construct some interesting topologies. Here, we report that the assembly of the squarate ligand with rare-earth ions can produce a series of (4, 8)-connected frameworks with the "smallest" scu type topology. Among these compounds, the Tb based analogue not only possesses a good proton conductivity, but also exhibits luminescence responses toward MnO4- and Cr2O72-, making it a candidate for multifunctional materials.

Growth modes of single-walled carbon nanotubes on catalysts.

Understanding the growth mechanism of single-walled carbon nanotubes (SWCNTs) and achieving selective growth requires insights into the catalyst structure-function relationship. Using an in situ aberration-corrected environmental transmission electron microscope, we reveal the effects of the state and structure of catalysts on the growth modes of SWCNTs. SWCNTs grown from molten catalysts via a vapor-liquid-solid process generally present similar diameters to those of the catalysts, indicating a size correlation between nanotubes and catalysts. However, SWCNTs grown from solid catalysts via a vapor-solid-solid process always have smaller diameters than the catalysts, namely, an independent relationship between their sizes. The diameter distribution of SWCNTs grown from crystalline Co7W6, which has a unique atomic arrangement, is discrete. In contrast, nanotubes obtained from crystalline Co are randomly dispersed. The different growth modes are linked to the distinct chiral selectivity of SWCNTs grown on intermetallic and monometallic catalysts. These findings will enable rational design of catalysts for chirality-controlled SWCNTs growth.

Editorial for the Special Issue: "Advanced Nanomaterials for Electrochemical Energy Conversion and Storage".

Developing efficient and low-cost energy conversion and storage devices and technologies is all-important issue in order to achieve a low-carbon society, whose performance essentially depends on the properties of materials [...].

Fe doped NiS nanosheet arrays grown on carbon fiber paper for a highly efficient electrocatalytic oxygen evolution reaction.

Developing efficient and low-cost non-noble metal catalysts for the oxygen evolution reaction (OER) is important for hydrogen production through water electrolysis. Herein, Fe doped NiS nanosheets directly grown on conductive carbon fiber paper (Fe-NiS@CFP) were fabricated through a two-step hydrothermal process. The microstructure, interface and electronic states of the prepared sample were modulated by Fe doping, exhibiting small internal and interface charge-transfer resistance. Benefiting from these factors, Fe-NiS@CFP shows superior electrocatalytic performance with an overpotential of 275 mV at 100 mA cm-2 and maintains the activity for at least 50 h as a working electrode for the OER. This work may provide insights into the design and fabrication of non-noble metal sulfide electrocatalysts.