Interface-mediated noble metal deposition on transition metal dichalcogenide nanostructures

Disentangling Competitive and Synergistic Chemical Reactivities During the Seeded Growth of High-Entropy Alloys on High-Entropy Metal Sulfide Nanoparticles

The seeded growth of one type of nanoparticle on the surface of another is foundational to synthesizing many multifunctional nanostructures. High-entropy nanoparticles that randomly incorporate five or more elements offer enhanced properties due to synergistic interactions. Incorporating high-entropy nanoparticles into seeded growth platforms is essential for merging their unique properties with the functional enhancements that arise from particle-particle interactions. However, the complex compositions of high-entropy materials complicate the seeded growth process due to competing particle growth and chemical reactivity pathways. Here, we design and synthesize a 36-member nanoparticle library to identify and disentangle these competitive interactions, ultimately defining chemical characteristics that underpin the seeded growth of high-entropy alloys on high-entropy metal sulfide nanoparticles. As a model system, we focus on (Cu,Zn,Co,In,Ga)S-SnPdPtRhIr, which combines a high-entropy metal sulfide semiconductor with a high-entropy alloy catalyst. We study the seeded growth of all possible pairwise combinations of Sn, Pd, Pt, Rh, Ir, and SnPdPtRhIr on the metal sulfides Cu1.8S, ZnS, Co9S8, CuInS2, CuGaS2, and (Cu,Zn,Co,In,Ga)S, which have comparable morphologies and sizes. Through these studies, we uncover unexpected chemical reactivities, including cation exchange, redox reactions, and diffusion. Reaction temperature, threshold reduction potentials, metal/sulfide chemical reactivity, and the relative strengths of the various bonds that could be formed during particle growth emerge as the primary factors that underpin seeded growth. Finally, we disentangle these competitive and synergistic chemical reactivities to generate a reactivity map that provides practical guidelines for achieving seeded growth in compositionally complex systems.

Heterostructured Pt-PbS Nanobelt Achieves Remarkable Direct Formic Acid Oxidation Catalysis

Developing efficient and CO-tolerant platinum (Pt)-based anodic catalysts is challenging for a direct formic acid fuel cell (DFAFC). Herein, we report heterostructured Pt-lead-sulfur (PtPbS)-based nanomaterials with gradual phase regulation as efficient formic acid oxidation reaction (FAOR) catalysts. The optimized Pt-PbS nanobelts (Pt-PbS NBs/C) display the mass and specific activities of 5.90 A mgPt-1 and 21.4 mA cm-2, 2.2/1.2, 1.5/1.1, and 36.9/79.3 times greater than those of PtPb-PbS NBs/C, Pt-PbSO4 NBs/C, and commercial Pt/C, respectively. Simultaneously, it exhibits a higher membrane electrode assembly (MEA) power density (183.5 mW cm-2) than commercial Pt/C (40.3 mW cm-2). This MEA stably operates at 0.4 V for 25 h, demonstrating a competitive potential of device application. The distinctive heterostructure endows the Pt-PbS NBs/C with optimized dehydrogenation steps and resisting the CO poisoning, thus presenting the remarkable FAOR performance. This work paves an effective avenue for creating high-performance anodic catalysts for fuel cells and beyond.

Electrophoretic Microplate Protein Identification Based on Gold Staining of Molybdenum Disulfide Hydrogels

Numerous high-performance nanotechnologies have been developed, but their practical applications are largely restricted by the nanomaterials' low stabilities and high operation complexity in aqueous substrates. Herein, we develop a simple and high-reliability hydrogel-based nanotechnology based on the in situ formation of Au nanoparticles in molybdenum disulfide (MoS2)-doped agarose (MoS2/AG) hydrogels for electrophoresis-integrated microplate protein recognition. After the incubation of MoS2/AG hydrogels in HAuCl4 solutions, MoS2 nanosheets spontaneously reduce Au ions, and the hydrogels are remarkably stained with the color of as-synthetic plasmonic Au hybrid nanomaterials (Au staining). Proteins can precisely mediate the morphologies and optical properties of Au/MoS2 heterostructures in the hydrogels. Consequently, Au staining-based protein recognition is exhibited, and hydrogels ensure the comparable stabilities and sensitivities of protein analysis. In comparison to the fluorescence imaging and dye staining, enhanced sensitivity and recognition performances of proteins are implemented by Au staining. In Au staining, exfoliated MoS2 semiconductors directly guide the oriented growth of plasmonic Au nanostructures in the presence of formaldehyde, showing environment-friendly features. The Au-stained hydrogels merge the synthesis and recognition applications of plasmonic Au nanomaterials. Significantly, the one-step incubation of the electrophoretic hydrogels leads to high simplicity of operation, largely challenging those multiple-step Ag staining routes which were performed with high complexity and formaldehyde toxicity. Due to its toxic-free, simple, and sensitive merits, the Au staining integrated with electrophoresis-based separation and microplate-based high-throughput measurements exhibits highly promising and improved practicality of those developing nanotechnologies and largely facilitates in-depth understanding of biological information.

Phase Engineering of Nanomaterials: Transition Metal Dichalcogenides

Crystal phase, a critical structural characteristic beyond the morphology, size, dimension, facet, etc., determines the physicochemical properties of nanomaterials. As a group of layered nanomaterials with polymorphs, transition metal dichalcogenides (TMDs) have attracted intensive research attention due to their phase-dependent properties. Therefore, great efforts have been devoted to the phase engineering of TMDs to synthesize TMDs with controlled phases, especially unconventional/metastable phases, for various applications in electronics, optoelectronics, catalysis, biomedicine, energy storage and conversion, and ferroelectrics. Considering the significant progress in the synthesis and applications of TMDs, we believe that a comprehensive review on the phase engineering of TMDs is critical to promote their fundamental studies and practical applications. This Review aims to provide a comprehensive introduction and discussion on the crystal structures, synthetic strategies, and phase-dependent properties and applications of TMDs. Finally, our perspectives on the challenges and opportunities in phase engineering of TMDs will also be discussed.

Atomic Au3Cu Palisade Interlayer in Core@Shell Nanostructures for Efficient Kirkendall Effect Mediation

Plasmonic Cu@semiconductor heteronanocrystals (HNCs) have many favorable properties, but the synthesis of solid structures is often hindered by the nanoscale Kirkendall effect. Herein, we present the use of an atomically thin Au3Cu palisade interlayer to reduce lattice mismatch and mediate the Kirkendall effect, enabling the successive topological synthesis of Cu@Au3Cu@Ag, Cu@Au3Cu@Ag2S, and further transformed solid Cu@Au3Cu@CdS core-shell HNCs via cation exchange. The atomically thin and intact Au3Cu palisade interlayer effectively modulates the diffusion kinetics of Cu atoms as demonstrated by experimental and theoretical investigations and simultaneously alleviates the lattice mismatch between Cu and Ag as well as Cu and CdS. The Cu@Au3Cu@CdS HNCs feature exceptional crystallinity and atomically organized heterointerfaces between the plasmonic metal and the semiconductor. This results in the efficient plasmon-induced injection of hot electrons from Cu@Au3Cu into the CdS shell, enabling the Cu@Au3Cu@CdS HNCs to achieve high activity and selectivity for the photocatalytic reduction of CO2 to CO.

Enzyme-free electrochemical sensor platforms based on transition metal nanostructures for clinical diagnostics

The detection of emergent biomarkers is of key significance in numerous clinical, biological, and biomedical fields. Specifically, the design and development of potent electrochemical lactic acid and glucose sensing platforms are especially in great demand in a variety of industries, including those involved in clinical analysis, biomedicine, biological, food, cosmetics, pharmaceuticals, leather, sports, and chemical industries. Nanostructured transition metal-derived materials have opened the door to electrochemical sensors and biosensors due to their advantages of high surface-to-volume ratio, surface reaction activity, catalytic activity, and strong adsorption capability. The primary aim of the present minireview is to highlight the advancement of enzyme-free electrochemical sensor platforms based on transition metal-derived nanostructures with high electrocatalytic activity and sensing performance towards lactic acid and glucose in practical samples. The preparation approaches, structural and composition monitoring, fabrication of sensing electrodes, catalytic activity, sensing performance in real samples, and the exploration of sensing mechanisms are majorly concentrated on in most of our recent research studies. Moreover, state-of-the-art transition metal-derived nanostructure-derived electrochemical sensor platforms, critical comparison of the analytical performance of the sensor platforms, and the future perspectives of the enzyme-free electrochemical sensor for clinical diagnostics are described.

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.

Morphological and Coordination Modulations in Iridium Electrocatalyst for Robust and Stable Acidic OER Catalysis

Proton exchange membrane water splitting (PEMWS) technology has high-level current density, high operating pressure, small electrolyzer-size, integrity, flexibility, and has good adaptability to the volatility of wind power and photovoltaics, but the development of both active and high stability of the anode electrocatalyst in acidic environment is still a huge challenge, which seriously hinders the promotion and application of PEMWS. In recent years, researchers have made tremendous attempts in the development of high-quality active anode electrocatalyst, and we summarize some of the research progress made by our group in the design and synthesis of PEMWS anode electrocatalysts with different nanostructures, and makes full use of electrocatalytic activity points to increase the inherent activity of Iridium (Ir) sites, and provides optimization strategies for the long-term non-decay of catalysts under high anode potential in acidic environments. At this stage, these research advances are expected to facilitate the research and technological progress of PEMWS, and providing some research ideas and references for future research on efficient and inexpensive PEMWS anode electrocatalysts.

Phase-dependent growth of Pt on MoS2 for highly efficient H2 evolution

Crystal phase is a key factor determining the properties, and hence functions, of two-dimensional transition-metal dichalcogenides (TMDs)1,2. The TMD materials, explored for diverse applications3-8, commonly serve as templates for constructing nanomaterials3,9 and supported metal catalysts4,6-8. However, how the TMD crystal phase affects the growth of the secondary material is poorly understood, although relevant, particularly for catalyst development. In the case of Pt nanoparticles on two-dimensional MoS2 nanosheets used as electrocatalysts for the hydrogen evolution reaction7, only about two thirds of Pt nanoparticles were epitaxially grown on the MoS2 template composed of the metallic/semimetallic 1T/1T' phase but with thermodynamically stable and poorly conducting 2H phase mixed in. Here we report the production of MoS2 nanosheets with high phase purity and show that the 2H-phase templates facilitate the epitaxial growth of Pt nanoparticles, whereas the 1T' phase supports single-atomically dispersed Pt (s-Pt) atoms with Pt loading up to 10 wt%. We find that the Pt atoms in this s-Pt/1T'-MoS2 system occupy three distinct sites, with density functional theory calculations indicating for Pt atoms located atop of Mo atoms a hydrogen adsorption free energy of close to zero. This probably contributes to efficient electrocatalytic H2 evolution in acidic media, where we measure for s-Pt/1T'-MoS2 a mass activity of 85 ± 23 A [Formula: see text] at the overpotential of -50 mV and a mass-normalized exchange current density of 127 A [Formula: see text] and we see stable performance in an H-type cell and prototype proton exchange membrane electrolyser operated at room temperature. Although phase stability limitations prevent operation at high temperatures, we anticipate that 1T'-TMDs will also be effective supports for other catalysts targeting other important reactions.

Fabrication of p-type 2D single-crystalline transistor arrays with Fermi-level-tuned van der Waals semimetal electrodes

High-performance p-type two-dimensional (2D) transistors are fundamental for 2D nanoelectronics. However, the lack of a reliable method for creating high-quality, large-scale p-type 2D semiconductors and a suitable metallization process represents important challenges that need to be addressed for future developments of the field. Here, we report the fabrication of scalable p-type 2D single-crystalline 2H-MoTe2 transistor arrays with Fermi-level-tuned 1T'-phase semimetal contact electrodes. By transforming polycrystalline 1T'-MoTe2 to 2H polymorph via abnormal grain growth, we fabricated 4-inch 2H-MoTe2 wafers with ultra-large single-crystalline domains and spatially-controlled single-crystalline arrays at a low temperature (~500 °C). Furthermore, we demonstrate on-chip transistors by lithographic patterning and layer-by-layer integration of 1T' semimetals and 2H semiconductors. Work function modulation of 1T'-MoTe2 electrodes was achieved by depositing 3D metal (Au) pads, resulting in minimal contact resistance (~0.7 kΩ·μm) and near-zero Schottky barrier height (~14 meV) of the junction interface, and leading to high on-state current (~7.8 μA/μm) and on/off current ratio (~105) in the 2H-MoTe2 transistors.

Impedimetric immunosensor for microalbuminuria based on a WS2/Au water-phase assembled nanocomposite

An electrochemical impedimetric biosensor for human serum albumin (HSA) determination is proposed. The biosensor is based on water-phase assembled nanocomposites made of 2D WS₂ nanoflakes and Au nanoparticles (AuNPs). The WS₂ has been produced using a liquid-phase exfoliation strategy assisted by sodium cholate, obtaining a water-stable suspension that allowed the straightforward decoration with AuNPs directly in the aqueous phase. The resulting WS₂/Au nanocomposite has been characterized by atomic force microscopy and Raman spectroscopy and, then, employed to modify screen-printed electrodes. Good electron-transfer features have been achieved. An electrochemical immunosensing platform has been assembled exploiting cysteamine-glutaraldehyde covalent chemistry for antibody (Ab) immobilization. The resulting immunosensor exhibited good sensitivity for HSA detection (LOD = 2 ng mL^-1), with extended linear range (0.005 - 100 µg mL^-1), providing a useful analytical tool for HSA determination in urine at relevant clinical ranges for microalbuminuria screening. The HSA quantification in human urine samples resulted in recoveries from 91.8 to 112.4% and was also reproducible (RSD < 7.5%, n = 3), with marked selectivity. This nanocomposite, thanks to the reliable performance and the ease of the assembling strategy, is a promising alternative for electrochemical immunosensing of health relevant markers.

Transition metal chalcogenides for next-generation energy storage

Transition-metal chalcogenide nanostructures provide a unique material platform to engineer next-generation energy storage devices such as lithium-ion, sodium-ion, and potassium-ion batteries and flexible supercapacitors. The transition-metal chalcogenide nanocrystals and thin films have enhanced electroactive sites for redox reactions and hierarchical flexibility of structure and electronic properties in the multinary compositions. They also consist of more earth-abundant elements. These properties make them attractive and more viable new electrode materials for energy storage devices compared to the traditional materials. This review highlights the recent advances in chalcogenide-based electrodes for batteries and flexible supercapacitors. The viability and structure-property relation of these materials are explored. The use of various chalcogenide nanocrystals supported on carbonaceous substrates, two-dimensional transition metal chalcogenides, and novel MXene-based chalcogenide heterostructures as electrode materials to improve the electrochemical performance of lithium-ion batteries is discussed. The sodium-ion and potassium-ion batteries offer a more viable alternative to lithium-ion technology as they consist of readily available source materials. Application of various transition metal chalcogenides such as MoS2, MoSe2, VS2, and SnSx, composite materials, and heterojunction bimetallic nanosheets composed of multi-metals as electrodes to enhance the long-term cycling stability, rate capability, and structural strength to counteract the large volume expansion during the ion intercalation/deintercalation processes is highlighted. The promising performances of layered chalcogenides and various chalcogenide nanowire compositions as electrodes for flexible supercapacitors are also discussed in detail. The review also details the progress made in new chalcogenide nanostructures and layered mesostructures for energy storage applications.

Recent innovations in the technology and applications of low-dimensional CuO nanostructures for sensing, energy and catalysis

Low-dimensional copper oxide nanostructures are very promising building blocks for various functional materials targeting high-demanded applications, including energy harvesting and transformation systems, sensing and catalysis. Featuring a very high surface-to-volume ratio and high chemical reactivity, these materials have attracted wide interest from researchers. Currently, extensive research on the fabrication and applications of copper oxide nanostructures ensures the fast progression of this technology. In this article we briefly outline some of the most recent, mostly within the past two years, innovations in well-established fabrication technologies, including oxygen plasma-based methods, self-assembly and electric-field assisted growth, electrospinning and thermal oxidation approaches. Recent progress in several key types of leading-edge applications of CuO nanostructures, mostly for energy, sensing and catalysis, is also reviewed. Besides, we briefly outline and stress novel insights into the effect of various process parameters on the growth of low-dimensional copper oxide nanostructures, such as the heating rate, oxygen flow, and roughness of the substrates. These insights play a key role in establishing links between the structure, properties and performance of the nanomaterials, as well as finding the cost-and-benefit balance for techniques that are capable of fabricating low-dimensional CuO with the desired properties and facilitating their integration into more intricate material architectures and devices without the loss of original properties and function.

Nonclassical Strong Metal-Support Interactions for Enhanced Catalysis

Strong metal-support interaction (SMSI), which encompasses reversible encapsulation and de-encapsulation and modulation of surface adsorption properties, imposes great impacts on the performance of heterogeneous catalysts. Recent development of SMSI has surpassed the prototypical encapsulated Pt-TiO₂ catalyst, affording a series of conceptually novel and practically advantageous catalytic systems. Here we provide our perspective on recent progress in nonclassical SMSIs for enhanced catalysis. Unravelling the structural complexity of SMSI necessitates the combination of multiple characterization techniques at different scales. Synthesis strategies leveraging chemical, photonic, and mechanochemical driving forces further expand the definition and application scope of SMSI. Exquisite structure engineering permits elucidation of the interface, entropy, and size effect on the geometric and electronic characteristics. Materials innovation places the atomically thin two-dimensional materials at the forefront of interfacial active site control. A broader space is awaiting exploration, where exploitation of metal-support interactions brings compelling catalytic activity, selectivity, and stability.

Interfacial Coordination Bonding-Assisted Redox Mechanism-Driven Highly Selective Precious Metal Recovery on Covalent-Functionalized Ultrathin 1T-MoS2

Rational design of functional material interfaces with well-defined physico-chemical-driven forces is crucial for achieving highly efficient interfacial chemical reaction dynamics for resource recovery. Herein, via an interfacial structure engineering strategy, precious metal (PM) coordination-active pyridine groups have been successfully covalently integrated into ultrathin 1T-MoS2 (Py-MoS2). The constructed Py-MoS2 shows highly selective interfacial coordination bonding-assisted redox (ICBAR) functionality toward PM recycling. Py-MoS2 shows state-of-the-art high recovery selectivity toward Au3+ and Pd4+ within 13 metal cation mixture solutions. The related recycling capacity reaches up to 3343.00 and 2330.74 mg/g for Au3+ and Pd4+, respectively. More importantly, above 90% recovery efficiencies have been achieved in representative PMs containing electronic solid waste leachate, such as computer processing units (CPU) and spent catalysts. The ICBAR mechanism developed here paves the way for interface engineering of the well-documented functional materials toward highly efficient PM recovery.

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.

Two-dimensional copper based colloidal nanocrystals: synthesis and applications

Two-dimensional (2D) semiconductor nanocrystals display unconventional physical and opto-electronic properties due to their ultrathin and unique electronic structures. Since the success of Cd-based photoemissive nanocrystals, the development of sustainable and low-cost nanocrystals with enhanced electronic and physical properties has become a central research theme. In this context, copper-based semiconductor 2D nanocrystals, the cost-effective and eco-friendly alternative, exhibit unique plasmonic resonance, transport properties, and high ionic conductivity beneficial for sensing, energy storage, conversion, and catalytic applications. This review summarizes recent progress in the colloidal synthesis, growth mechanisms, properties, and applications of 2D copper-based nanostructures with tunable compositions, dimensions, and crystal phases. We highlight the growth mechanisms concerning their shape evolution in two dimensions. We analyse the effectiveness of cation exchange as a tool to synthesize multinary nanocrystals. Based on the preparation of Cu-based chalcogenide and non-chalcogenide compositions, we discuss synthesis control achieved via colloidal approaches to allow dimension tunability, phase engineering, and plasmonic and thermoelectric property optimization. Furthermore, their potential in various applications of catalysis, energy storage, and sensing is reviewed. Finally, we address the current challenges associated with 2D Cu-based nanocrystal development and provide an outlook pertaining to unexplored research areas.

Fe doped MoS2/polypyrrole microtubes towards efficient peroxidase mimicking and colorimetric sensing application

Molybdenum disulfide (MoS2) nanosheets have been found to exhibit intrinsic peroxidase-like activity that could be applied in colorimetric sensing platforms. However, their poor conductivity and few exposed edge sites often lead to poor catalytic activity, impeding the application of MoS2 nanosheets in enzyme-like catalysis. Here, a novel strategy was developed to selectively deposit Fe-doped MoS2 nanosheets on polypyrrole microtubes to obtain Fe-MoS2@PPy microtubes to address these issues. In the synthesized Fe-MoS2@PPy microtubes, PPy microtubes can not only be used as a conductive support to promote the electron transfer, but also greatly alleviate the aggregations of MoS2 nanosheets, and thus improve the enzyme-like activity. Meanwhile, additional active sites, formed by Fe doping, also endow the catalyst with excellent activity in enzyme-like catalysis. Notably, in the process of sulfidation, the dissolution, redistribution and diffusion result in the disappearance of MoO3@FeOOH cores and the formation of Fe doped MoS2 nanosheets, which significantly facilitate the deposition of Fe-doped MoS2 nanosheets on PPy microtubes. On the basis of the high peroxidase-like catalytic efficiency of the Fe-MoS2@PPy microtubes, a simple and convenient colorimetric strategy for the rapid and sensitive detection of L-cysteine has been developed. This strategy introduces both the PPy layer and Fe doping to increase the conductivity and the density of active sites of MoS2 nanosheets, thus enhancing the catalytic activity and stability. More importantly, Fe-MoS2@PPy microtubes could be used as a good support for loading other materials such as Au and Ag nanoparticles (NPs), forming ternary Fe-MoS2/Ag, Au@PPy nanotubes. This work offers an opportunity to develop low-cost and highly active MoS2-based nanocomposites for promising potential applications in electrochemical energy conversion and medical diagnostics.

Bidirectional and reversible tuning of the interlayer spacing of two-dimensional materials

Interlayer spacing is expected to influence the properties of multilayer two-dimensional (2D) materials. However, the ability to non-destructively regulate the interlayer spacing bidirectionally and reversibly is challenging. Here we report the preparation of 2D materials with tunable interlayer spacing by introducing active sites (Ce ions) in 2D materials to capture and immobilize Pt single atoms. The strong chemical interaction between active sites and Pt atoms contributes to the intercalation behavior of Pt atoms in the interlayer of 2D materials and further promotes the formation of chemical bonding between Pt atom and host materials. Taking cerium-embedded molybdenum disulfide (MoS2) as an example, intercalation of Pt atoms enables interlayer distance tuning via an electrochemical protocol, leading to interlayer spacing reversible and linear compression and expansion from 6.546 ± 0.039 Å to 5.792 ± 0.038 Å (~11 %). The electronic property evolution with the interlayer spacing variation is demonstrated by the photoluminescence (PL) spectra, delivering that the well-defined barrier between the multilayer and monolayer layered materials can be artificially designed.

A General Synthesis Strategy for Hollow Metal Oxide Microspheres Enabled by Gel-Assisted Precipitation

Hollow metal oxide microspheres (HMMs) have drawn enormous attention in different research fields. Reliable and scalable synthetic protocols applicable for a large variety of metal oxides are in emergent demand. Here we demonstrated that polymer hydrogel, such as the resorcinol formaldehyde (RF) one, existed as an efficient synthetic platform to build HMMs. Specifically, the RF gel forms stacked RF microspheres enlaced with its aqueous phase, where the following evaporation of the highly dispersed water leads to a gel-assisted precipitation (GAP) of the dissolved metal precursor onto the embedded polymeric solids suited for the creation of HMMs. By taking advantage of the structural features of hydrogel, this synthesis design avoids the delicate control on the usually necessitated coating process and provides a simple and effective synthetic process versatile for functional HMMs, particularly Nb₂ O₅ as a high-performance electrode material in Li-ion intercalation pseudocapacitor.

Scalable production of intrinsic WX2(X = S, Se, Te) quantum sheets for efficient hydrogen evolution electrocatalysis

Mass production of transition-metal dichalcogenides has attracted much attention to replace platinum-based catalysts for the hydrogen evolution reaction (HER). Herein, we demonstrate a general strategy for the scalable production of the intrinsic tungsten dichalcogenide (WX₂(X = S, Se, Te)) quantum sheets (QSs) by an all-physical top-down method. The method combines silica-assisted ball-milling and sonication-assisted solvent exfoliation and thus enables production of WS₂QSs, WSe₂QSs, and WTe₂QSs in exceedingly high yields of 28.2, 21.3, 19.9 wt%, respectively. The WX₂QSs are confirmed as intrinsic and defect-free, which could be determinative to their improved HER performance. The overpotentials of 285, 331, 435 mV at the current density of 10 mA cm^-2and Tafel slopes of 116, 78, 162 mV dec^-1in acidic media, as well as charge transfer resistance values of 171, 242, 1973 Ω, are derived for WS₂QSs, WSe₂QSs, and WTe₂QSs, respectively, which are much better than those of bulk materials. The WX₂QSs exhibit high stability during the electrocatalysis as well. This work offers a powerful approach for fabrication of intrinsic QSs as efficient and robust electrocatalysts.

General Route to Colloidal Nanocrystal Clusters with Precise Hierarchical Control via Star-like Nanoreactors

A colloidal nanocrystal cluster (CNC) is a hierarchical nanostructure formed by clustering several nanocrystals into one nano-ensemble, which may exhibit unique optical or catalytic properties different from individual nanocrystals owing to the mutual interactions among neighboring component nanocrystals. However, there is still no universal synthetic route that could be applicable to diverse material compositions with precisely controlled hierarchical structures (i.e., nanocrystal number density, component nanocrystal size, and overall diameter of the CNC) up to now. Herein, a general and novel synthetic strategy was reported for crafting a wide range of inorganic CNCs (i.e., noble metal, semiconductor, and metal oxide) via utilizing amphiphilic star-like poly(4-vinylpyridine)-block-polystyrene diblock copolymers as nanoreactors prepared by sequential atom transfer radical polymerization. The hierarchical structure of rationally designed CNCs could be readily tailored by varying the P4VP molecular weight of star-like nanoreactors and the parameter optimization during the CNC preparation process, which was inaccessible by conventional synthetic methods.

Silica-Enveloped 2D-Sheet-to-Nanocrystals Conversion for Resilient Catalytic Dry Reforming of Methane

Here, lamellar confinement strategy is introduced for "sheet-to-nanocrystals (NCs)" conversion within a 2D-SiO₂ envelope, which constructs a catalytic nanocartridge holding a platoon of isolated and in-plane-aligned ultrasmall Ni-NCs, performing as a robust and coking-resistant catalytic system for dry reforming of methane. Overcoming the problem of unavoidable bulk crystal growth from multiple sheets-stack or sheet-on-open-support, silica bilayer-encasing tightly clamps the atomic-thin Ni(OH)₂ -nanosheet during thermal conversion and further hinders the migratory fusion of the resultant Ni-NCs. Upon heating-cooling cycle, the flapping silica envelope clutches the Ni-NCs like "eggs in a carton," subsequently, ensuring their thermal stability. Owing to the unique 2D-enveloped rigid architecture, Ni-NCs can circumvent sintering and coke deposition while tolerating the high temperatures (>700 °C) for long operation (>100 h), affording high conversions to syngas.

Gold nanodot assembly within a cobalt chalcogenide nanoshell: Promotion of electrocatalytic activity

The assembly of functional nanoparticles within materials with unique architectures can improve the interfacial surfaces, defects, and active sites, which are key factors for the designing novel nanocatalysts. Nano metal-organic framework (NMOF) can be employed to fabricate nanodots-confined nanohybrids for use in electrocatalytic processes. Herein, we report a controlled synthesis of gold nanodot assembly within cobalt chalcogenide nanoshell (dots-in-shell Au/Co_xS_y nanohybrids). A cobalt-based NMOF (the cobalt-based zeolite imidazole framework, ZIF-67) is used as a versatile sacrificial template to yield dots-in-shell Au/Co_xS_y nanohybrids. Due to the synergistic effect of the well-dispersed Au nanodots and the thin Co_xS_y nanoshell, the obtained dots-in-shell Au/Co_xS_y nanohybrids exhibit enhanced performance for the oxygen evolution reaction (OER) with low overpotential values at a current density of 10 mA cm^-2 and a small Tafel slope (343 mV and 62 mV dec^-1, respectively).

High-entropy materials for catalysis: A new frontier

Entropy plays a pivotal role in catalysis, and extensive research efforts have been directed to understanding the enthalpy-entropy relationship that defines the reaction pathways of molecular species. On the other side, surface of the catalysts, entropic effects have been rarely investigated because of the difficulty in deciphering the increased complexities in multicomponent systems. Recent advances in high-entropy materials (HEMs) have triggered broad interests in exploring entropy-stabilized systems for catalysis, where the enhanced configurational entropy affords a virtually unlimited scope for tailoring the structures and properties of HEMs. In this review, we summarize recent progress in the discovery and design of HEMs for catalysis. The correlation between compositional and structural engineering and optimization of the catalytic behaviors is highlighted for high-entropy alloys, oxides, and beyond. Tuning composition and configuration of HEMs introduces untapped opportunities for accessing better catalysts and resolving issues that are considered challenging in conventional, simple systems.

Colloidal Nanostructures of Transition-Metal Dichalcogenides

ConspectusLayered transition-metal dichalcogenides (TMDs) are intriguing two-dimensional (2D) compounds where metal and chalcogen atoms are covalently bonded in each monolayer, and the monolayers are held together by weak van der Waals forces. Distinct from graphene, which is chemically inert, layered TMDs exhibit a wide range of electronic, optical, catalytic, and magnetic properties dependent upon their compositions, crystal structures, and thicknesses, which make them fundamentally and technologically important. TMD nanostructures are traditionally synthesized using gas-phase chemical deposition methods, which are typically limited to small-scale samples of substrate-bound planar materials. Colloidal synthesis has emerged as an alternative synthesis approach to enable the scalable synthesis of free-standing TMDs. The judicious selection of precursors, solvents, and capping ligands together with the optimization of synthesis parameters such as concentrations and temperatures leads to the fabrication of colloidal TMD nanostructures exhibiting tunable properties. In addition, understanding the formation and transformation of TMD nanostructures in solution contributes to the discovery of important structure-function relationships, which may be extendable to other anisotropic systems.In this Account, we summarize recent progress in the colloidal synthesis, characterization, and applications of TMD nanostructures with tunable compositions, structures, and thicknesses. On the basis of the preparation of Mo- and W-based disulfide, diselenide, and ditelluride nanostructures, we discuss examples of phase engineering where various metastable TMD compounds can be directly accessed at low temperatures in solution. We also analyze the chemistry involved in broadly tuning the composition across the MoSe₂-WSe₂, WS₂-WSe₂, and MoTe₂-WTe₂ solid solutions as well as atomic-level microscopic characterization and the resulting composition-tunable properties. We then highlight how the high densities of defects in the colloidally synthesized TMD nanostructures enable unique catalytic properties, including their ability to facilitate the selective hydrogenation of substituted nitroarenes using molecular hydrogen. Finally, using this library of colloidal TMD nanostructures as substrates, we discuss the pathways by which noble metals deposit onto them in solution. We highlight the importance of the relative strengths of the interfacial metal-chalcogen bonds in determining the sizes and morphologies of the deposited noble metal components. These synthesis capabilities for colloidal TMD nanostructures, which have been generalized to a library of composition-tunable phases, enable new systematic studies of structure-property relationships and chemical reactivity in this important class of 2D materials.

Manipulation of Interfacial Diffusion for Controlling Nanoscale Transformation

The unprecedented development of inorganic nanostructure synthesis has paved the way toward their broad applications in areas such as food science, agroforestry, energy conversion, and biomedicine. The precise manipulation of the nucleation and subsequent growth has been recognized as the central guiding principle for controlling the size and morphology of the nanostructures. However, conventional colloid syntheses based on direct precipitation reactions still have limitations in their versatility and extendibility. The crystal structure of a material determines the limited number of possible morphologies that its nanostructures can adopt. Further, as nucleation and growth kinetics are sensitive to not only the nature of the precipitation reactions but also ligands and ripening effect, rigorous control of reaction conditions must be established for every specific synthesis. In addition, multiple experimental parameters are entangled with each other, thereby requiring rigorous control of all reaction conditions. As a result, it is usually challenging to extend a synthetic recipe from one material to another. As an alternative method, the direct transformation of existing nanostructures into target ones has become an effective and robust approach capable of creating various complex nanostructures that are otherwise challenging to obtain using conventional methods. To this end, an in-depth understanding of nanoscale transformation toward the synthesis of inorganic nanostructures with diverse properties and applications is highly desirable.In this Account, we aim to reveal the critical effect of the interfacial diffusion on controlled nanoscale transformation. We first discuss how the interdiffusion rates determine the morphology and properties of bimetallic nanostructures. While equal interdiffusion rates lead to perfect mixing and generate fully alloyed nanostructures, interdiffusion at unequal rates creates vacancies in the fast diffusion side, which may cause dramatic morphological transformation to the nanostructures. Then, we introduce interfacial reactions, including the Kirkendall cavitation process, elimination reaction, and solid-state reaction, to promote the unbalanced interdiffusion and generalize nanoscale transformations in materials of various compositions, morphologies, and crystal structures. Finally, we discuss the use of capping ligands to inhibit the diffusion of atoms on one side of the interface in order to enable selective etching or transformation of the nanostructures. By modifying the nanostructured surface with specific capping ligands, the diffusion of surface atoms is restricted. When nanoparticles undergo chemical reactions (such as etching or heating), the outward diffusion of substances dominates, thereby successfully achieving chemical and morphological transformations. We believe that controlled interfacial diffusion can effectively manipulate nanoscale transformations, thus providing new strategies for the custom synthesis of multifunctional nanomaterials for various specific applications.

Unveiling surface charge on chalcogen atoms toward the high aspect-ratio colloidal growth of two-dimensional transition metal chalcogenides

Controlling surface energies of each facet is essential for the anisotropic growth of two-dimensional transition metal chalcogenides (TMCs). However, it is a challenge due to stronger binding energies of ligand head groups to the edge facets compared to the planar facets. Herein, we demonstrate that the adsorption of ligands on metal positions can induce partial electron localization on the chalcogen sites, and then accelerate metal-chalcogen bond formation for enhanced anisotropic growth of nanosheets. And only in the case of trioctylphosphine oxide (TOPO)-adsorbed nanosheets, surface polarization can be unveiled on the surface of the colloidal nanosheets due to restricted development of nonpolar ligand shells by the steric effects of the ligands. Moreover, density functional theory (DFT) calculation results reveal that the decrease of surface energy on the (100) edge facets as well as the increase on the (001) basal facets by the adsorption of triorganylphosphine oxide also contribute to the preferentially lateral growth. As a result, various 2D TMCs, including MoSe2, WSe2, and SnSe2 synthesized with TOPO, show enhanced anisotropic growth.

Tuning the electronic structures of self-supported vertically aligned CoFe LDH arrays integrated with Ni foam toward highly efficient electrocatalytic water oxidation

The developed Ni/CoFe LDH as an anode can provide a current density of 10 mA cm⁻² at 1.532 V vs. RHE, as well as remarkable operational stability, representing the best yet reported noble-metal-free water oxidation electrode.

Self-regenerative noble metal catalysts supported on high-entropy oxides

Discovery of anti-sintering noble metal catalysts is challenging, as supported noble metal species tend to aggregate at high temperatures, leading to severely deteriorated catalytic performances. Here we show that 1 wt% of noble metal species including Au, Pd and Ru can be incorporated into high-entropy oxides (HEOs) through entropy stabilization at 900 °C in air. A reversible temperature-dependent dissolution-exsolution process is observed for Au-HEO. Further correlation with distinct CO oxidation capabilities demonstrates the potential to utilize the entropy effect to access self-regenerative catalysts for catalytic reactions.

Ultrafast formation of an FeOOH electrocatalyst on Ni for efficient alkaline water and urea oxidation

We report FeOOH supported on Ni foam which enables highly efficient UOR electrocatalysis and can be readily produced through a hydrolysis reaction. Our developed UOR catalyst as the anode can provide a current density of 200 mA cm^-2 at 1.427 V vs. RHE, as well as remarkable operational stability, representing the best yet reported noble metal-free urea electrolyser.

Dynamic Surface Reconstruction of Single-Atom Bimetallic Alloy under Operando Electrochemical Conditions

The atomic-level understanding of the dynamic evolution of the surface structure of bimetallic nanoparticles under industrially relevant operando conditions provides a key guide for improving their catalytic performance. Here, we exploit operando X-ray absorption fine structure spectroscopy to determine the dynamic surface reconstruction of Cu/Au bimetallic alloy where single-atom Cu was embedded on the Au nanoparticle, under electrocatalytic conditions. We identify the migration of isolated Cu atoms from the vertex position of the Au nanoparticle to the stable (100) plane of the Au first atom layer, when the reduction potential is applied. Density functional theory calculations reveal that the surface atom migration would significantly modulate the Au electronic structure, thus serving as the real active site for the catalytic performance. These findings demonstrate the real structural change under electrochemical conditions and provide guidance for the rational design of high-activity bimetallic nanocatalysts.

Mo-Based Layered Nanostructures for the Electrochemical Sensing of Biomolecules

Mo-based layered nanostructures are two-dimensional (2D) nanomaterials with outstanding characteristics and very promising electrochemical properties. These materials comprise nanosheets of molybdenum (Mo) oxides (MoO2 and MoO3), dichalcogenides (MoS2, MoSe2, MoTe2), and carbides (MoC2), which find application in electrochemical devices for energy storage and generation. In this feature paper, we present the most relevant characteristics of such Mo-based layered compounds and their use as electrode materials in electrochemical sensors. In particular, the aspects related to synthesis methods, structural and electronic characteristics, and the relevant electrochemical properties, together with applications in the specific field of electrochemical biomolecule sensing, are reviewed. The main features, along with the current status, trends, and potentialities for biomedical sensing applications, are described, highlighting the peculiar properties of Mo-based 2D-nanomaterials in this field.

Site-specific electrodeposition enables self-terminating growth of atomically dispersed metal catalysts

The growth of atomically dispersed metal catalysts (ADMCs) remains a great challenge owing to the thermodynamically driven atom aggregation. Here we report a surface-limited electrodeposition technique that uses site-specific substrates for the rapid and room-temperature synthesis of ADMCs. We obtained ADMCs by the underpotential deposition of a non-noble single-atom metal onto the chalcogen atoms of transition metal dichalcogenides and subsequent galvanic displacement with a more-noble single-atom metal. The site-specific electrodeposition enables the formation of energetically favorable metal-support bonds, and then automatically terminates the sequential formation of metallic bonding. The self-terminating effect restricts the metal deposition to the atomic scale. The modulated ADMCs exhibit remarkable activity and stability in the hydrogen evolution reaction compared to state-of-the-art single-atom electrocatalysts. We demonstrate that this methodology could be extended to the synthesis of a variety of ADMCs (Pt, Pd, Rh, Cu, Pb, Bi, and Sn), showing its general scope for functional ADMCs manufacturing in heterogeneous catalysis.

Holey Pt Nanosheets on NiFe-Hydroxide Laminates: Synergistically Enhanced Electrocatalytic 2D Interface toward Hydrogen Evolution Reaction

Next-generation electrocatalysts with smart integrated designs, maximizing the chemical cascade synergy for sustainable hydrogen production, are needed to address the urgent environmental threats, but scalable synthesis of precisely architectured nanohybrids rendering a few-nanometer interfacial controllability to augment the catalytic reactivity and operational stability is a major bottleneck. Herein, by inventing a surface-confined lateral growth of nanometer-thin and nanoporous two-dimensional (2D)-Pt on NiFe-LDH nanosheets, a highly reactive 2D-2D interfacially integrated nanoplatform is synthesized for an alkaline hydrogen evolution reaction (HER) which not only extracts high Pt-atomic utilization efficiency but also synergistically accelerates the water dissociation and hydrogen generation cascade on the colocalized Pt/M(OH)_x active sites, endowing a 6.1-fold higher Pt mass activity than 20% Pt/C and also empowers a record-high HER operational stability for 50 h, due to the chemically enforced lamellar architecture. This work offers a gateway to produce active metal nanosheets tailored with a suitable active-template surface in order to invent and enforce futuristic catalysis technologies.

Layered MoS2 defect-driven in situ synthesis of plasmonic gold nanocrystals visualizes the planar size and interfacial diversity

Current defect theories significantly guide broad research progress, whereas the recognition of defect status remains challenging. Herein, MoS2 defect type, density and exposed state are visually identified with a reagent indicator of HAuCl4. Mo-terminated defects spontaneously reduce [AuCl4]- anions and oxidized Mo species are dissociated. Consequently, MoS2 edges guide the epitaxial branch of Au nanocrystals (NCs), followed by sequential growths at their planar defects. The size-evolution processes of LaMer growth and planar packages of the aggregative growth of Au/MoS2 nanoseeds result in the occupation of Au atomic layers on heterostructures. Consequently, shell-core hybrids are presented with localized surface plasmon resonance characteristics. The mechanism is systematically explored via the discriminated performance of plasmonic characteristics of Au nanostructures on semiconducting MoS2 substrates. With plasmonic identification, defect-associated size and interfacial diversities of MoS2 are visually information-rich. Tunable morphologies and synergistic optical characteristics of plasmonic semiconductor heterostructures inspire many more applications through the edge and planar defects intrinsic in layered MoS2.

Fabrication of noble metal nanoparticles decorated on one dimensional hierarchical polypyrrole@MoS2 microtubes

Herein, we present a facile strategy to fabricate noble metal (Ag, Au, Pd) decorated on PPy@MoS₂ microtubes. As a proof of application, the ternary PPy@MoS₂@Au hybrids reveal excellent enzyme-like catalytic performance.