Tailoring chemical bonds to design unconventional glasses.

Glasses are commonly described as disordered counterparts of the corresponding crystals; both usually share the same short-range order, but glasses lack long-range order. Here, a quantification of chemical bonding in a series of glasses and their corresponding crystals is performed, employing two quantum-chemical bonding descriptors, the number of electrons transferred and shared between adjacent atoms. For popular glasses like SiO2, GeSe2, and GeSe, the quantum-chemical bonding descriptors of the glass and the corresponding crystal hardly differ. This explains why these glasses possess a similar short-range order as their crystals. Unconventional glasses, which differ significantly in their short-range order and optical properties from the corresponding crystals are only found in a distinct region of the map spanned by the two bonding descriptors. This region contains crystals of GeTe, Sb2Te3, and GeSb2Te4, which employ metavalent bonding. Hence, unconventional glasses are only obtained for solids, whose crystals employ theses peculiar bonds.

Characteristic Plasmon Energies for 2D In2Se3 Phase Identification at Nanoscale.

Two-dimensional (2D) materials with competing polymorphs offer remarkable potential to switch the associated 2D functionalities for novel device applications. Probing their phase transition and competition mechanisms requires nanoscale characterization techniques that can sensitively detect the nucleation of secondary phases down to single-layer thickness. Here we demonstrate nanoscale phase identification on 2D In2Se3 polymorphs, utilizing their distinct plasmon energies that can be distinguished by electron energy-loss spectroscopy (EELS). The characteristic plasmon energies of In2Se3 polymorphs have been validated by first-principles calculations, and also been successfully applied to reveal phase transitions using in situ EELS. Correlating with in situ X-ray diffraction, we further derive a subtle difference in the valence electron density of In2Se3 polymorphs, consistent with their disparate electronic properties. The nanometer resolution and independence of orientation make plasmon-energy mapping a versatile technique for nanoscale phase identification on 2D materials.

Two-Dimensional M-Chalcogene Family with Tunable Superconducting, Topological, and Magnetic Properties.

An interesting question is whether chalcogen atoms can emulate the role of carbon or boron elements stabilized between two transition metal layers, as observed in MXenes or MBenes. Here, we predict a new family of two-dimensional ternary compounds M4XY2 (where M = Pd, Y, Zr, etc.; X = S, Se, Te; and Y = Cl, Br, I), named M-chalcogene. Through first-principles calculations, we reveal diverse physical properties in these compounds, including superconducting, topological, and magnetic characteristics, where the bilayer transition metals play crucial roles. Moreover, the expected helical edge states and superconducting transition temperatures in Pd4SCl2 can be finely tuned by strains. Additionally, the Ti4SCl2 is predicted to be a topological insulator and shows promise as a gas sensor candidate for certain exotic gases. Our findings expand two-dimensional material families and provide promising platforms for diverse physical phenomena with efficient tunability by external stimuli for various applications.

Polysulfide Anions [Sx]2- (x = 2, 3, 4, 5): Promising Functional Building Units for Infrared Nonlinear Optical Materials.

Infrared nonlinear optical (IR NLO) materials play significant roles in laser technology. The novel functional building units (FBUs) are of great importance in constructing NLO materials with strong second harmonic generation (SHG). Herein, polysulfide anion [Sx]2- (x = 2, 3, 4, 5) units are investigated on NLO-related properties and structure-performance relationships. Theoretical calculations uncover that the [Sx]2- (x = 2, 3, 4, 5) units are potential IR NLO FBUs with large polarizability anisotropy (δ), hyperpolarizability (ß) and wide HOMO-LUMO gap. Fourteen crystals including [Sx]2- (x = 2, 3, 4, 5) units are calculated and analyzed. The results show that these units can result in a wide IR transmittance range, significant SHG effects, wide band gap Eg (Na2S4: Eg = 3.09 eV), and large birefringence Δn [BaS3 (P21212): Δn = 0.70]. More importantly, it is highlighted that the crystal materials including with [Sx]2- (x = 2, 3, 4, 5) groups are good candidates for the exploration of the outstanding IR NLO materials.

Precursor Engineering of Solution-Processed Sb2 S3 Solar Cells.

Antimony-based chalcogenides have emerged as promising candidates for next-generation thin film photovoltaics. Particularly, binary Sb2 S3 thin films have exhibited great potential for optoelectronic applications, due to the facile and low-cost fabrication, simple composition, decent charge transport and superior stability. However, most of the reported efficient Sb2 S3 solar cells are realized based on chemical bath deposition and hydrothermal methods, which require large amount of solution and are normally very time-consuming. In this work, Ag ions are introduced within the Sb2 S3 sol-gel precursors, and effectively modulated the crystallization and charge transport properties of Sb2 S3 . The crystallinity of the Sb2 S3 crystal grains are enhanced and the charge carrier mobility is increased, which resulted improved charge collection efficiency and reduced charge recombination losses, reflected by the greatly improved fill factor and open-circuit voltage of the Ag incorporated Sb2 S3 solar cells. The champion devices reached a record high power conversion efficiency of 7.73% (with antireflection coating), which is comparable with the best photovoltaic performance of Sb2 S3 solar cells achieved based on chemical bath deposition and hydrothermal techniques, and pave the great avenue for next-generation solution-processed photovoltaics.

Janus Zn-IV-VI: Robust Photocatalysts with Enhanced Built-In Electric Fields and Strain-Regulation Capability for Water Splitting.

The use of 2D materials to produce hydrogen (H2 ) fuel via photocatalytic water splitting has been intensively studied. However, the simultaneous fulfillment of the three essential requirements-high photon utilization, rapid carrier transfer, and low-barrier redox reactions-for wide-pH-range production of H2 still poses a significant challenge with no additional modulation. By employing the first-principles calculations, it has been observed that the Janus ZnXY2 structures (X = Si/Ge/Sn, Y = S/Se/Te) exhibit significantly enhanced built-in electric fields (0.20-0.36 eV Å-1 ), which address the limitations intrinsically. Compared to conventional Janus membranes, the ductile ZnSnSe2 and ZnSnTe2 monolayers have stronger regulation of electric fields, resulting in improved electron mobility and excitonic nature (Ebinding = 0.50/0.35 eV). Both monolayers exhibit lower energy barriers of hydrogen evolution reaction (HER, 0.98/0.86 eV, pH = 7) and resistance to photocorrosion across pH 0-7. Furthermore, the 1% tensile strain can further boost visible light utilization and intermediate absorption. The optimal AC-type bilayer stacking configuration is conducive to enhancing electric fields for photocatalysis. Overall, Janus ZnXY2 membranes overcome the major challenges faced by conventional 2D photocatalysts via intrinsic polarization and external amelioration, enabling efficient and controllable photocatalysis without the need for doping or heterojunctions.

MOCHAs: An Emerging Class of Materials for Photocatalytic H2 Production.

Production of green hydrogen (H2) is a sustainable process able to address the current energy crisis without contributing to long-term greenhouse gas emissions. Many Ag-based catalysts have shown promise for light-driven H2 generation, however, pure Ag-in its bulk or nanostructured forms-suffers from slow electron transfer kinetics and unfavorable Ag─H bond strength. It is demonstrated that the complexation of Ag with various chalcogenides can be used as a tool to optimize these parameters and reach improved photocatalytic performance. In this work, metal-organic-chalcogenolate assemblies (MOCHAs) are introduced as effective catalysts for light-driven hydrogen evolution reaction (HER) and investigate their performance and structural stability by examining a series of AgXPh (X = S, Se, and Te) compounds. Two catalyst-support sensitization strategies are explored: by designing MOCHA/TiO2 composites and by employing a common Ru-based photosensitizer. It is demonstrated that the heterogeneous approach yields stable HER performance but involves a catalyst transformation at the initial stage of the photocatalytic process. In contrast to this, the visible-light-driven MOCHA-dye dyad shows similar HER activity while also ensuring the structural integrity of the MOCHAs. The work shows the potential of MOCHAs in constructing photosystems for catalytic H2 production and provides a direct comparison between known AgXPh compounds.

Electrochemical Deposition for Cultivating Nano- and Microstructured Electroactive Materials for Supercapacitors: Recent Developments and Future Perspectives.

The globe is currently dealing with serious issues related to the world economy and population expansion, which has led to a significant increase in the need for energy. One of the most promising energy devices for the next generation of energy technology is the supercapacitor (SC). Among the numerous nanostructured materials examined for SC electrodes, inorganic nanosheets are considered to be the most favorable electrode materials because of their excellent electrochemical performance due to their large surface area, very low layer thickness, and tunable diverse composition. Various inorganic nanosheets (NS) such as metal oxides, metal chalcogenides, metal hydroxides, and MXenes show substantial electrochemical activity. Herein, a comprehensive survey of inorganic NS arrays synthesized through the electrodeposition method is reported with the discussion on detailed growth mechanism and their application in the fabrication of SC electrodes/devices for powering flexible and wearable electronics appliances. To begin with, the first section will feature the various types of electrodeposition working mechanism, SC types and their working mechanisms, importance of nanosheet structure for SCs. This review gives a profound interpretation of supercapacitor electrode materials and their performances in different domains. Finally, a perspective on NS array through electrodeposition method applications in diverse fields is extensively examined.

Vacancy Engineering in 2D Transition Metal Chalcogenide Photocatalyst: Structure Modulation, Function and Synergy Application.

Transition metal chalcogenides (TMCs) are widely used in photocatalytic fields such as hydrogen evolution, nitrogen fixation, and pollutant degradation due to their suitable bandgaps, tunable electronic and optical properties, and strong reducing ability. The unique 2D malleability structure provides a pre-designed platform for customizable structures. The introduction of vacancy engineering makes up for the shortcomings of photocorrosion and limited light response and provides the greatest support for TMCs in terms of kinetics and thermodynamics in photocatalysis. This work reviews the effect of vacancy engineering on photocatalytic performance based on 2D semiconductor TMCs. The characteristics of vacancy introduction strategies are summarized, and the development of photocatalysis of vacancy engineering TMCs materials in energy conversion, degradation, and biological applications is reviewed. The contribution of vacancies in the optical range and charge transfer kinetics is also discussed from the perspective of structure manipulation. Vacancy engineering not only controls and optimizes the structure of the TMCs, but also improves the optical properties, charge transfer, and surface properties. The synergies between TMCs vacancy engineering and atomic doping, other vacancies, and heterojunction composite techniques are discussed in detail, followed by a summary of current trends and potential for expansion.

Breaking Through the Trade-Off Between Wide Band Gap and Large SHG Coefficient in Mercury-Based Chalcogenides for IR Nonlinear Optical Application.

It is substantially challenging for non-centrosymmetric (NCS) Hg-based chalcogenides for infrared nonlinear optical (IR-NLO) applications to realize wide band gap (Eg > 3.0 eV) and sufficient phase-matching (PM) second-harmonic-generation intensity (deff > 1.0 × benchmark AgGaS2 ) simultaneously due to the inherent incompatibility. To address this issue, this work presents a diagonal synergetic substitution strategy for creating two new NCS quaternary Hg-based chalcogenides, AEHgGeS4 (AE = Sr and Ba), based on the centrosymmetric (CS) AEIn2 S4 . The derived AEHgGeS4 displays excellent NLO properties such as a wide Eg (≈3.04-3.07 eV), large PM deff (≈2.2-3.0 × AgGaS2 ), ultra-high laser-induced damage threshold (≈14.8-15 × AgGaS2 ), and suitable Δn (≈0.19-0.24@2050 nm), making them highly promising candidates for IR-NLO applications. Importantly, such excellent second-order NLO properties are primarily attributed to the synergistic combination of tetrahedral [HgS4 ] and [GeS4 ] functional primitives, as supported by detailed theoretical calculations. This study reports the first two NCS Hg-based materials with well-balanced comprehensive properties (i.e., Eg > 3.0 eV and deff > 1.0 × benchmark AgGaS2 ) and puts forward a new design avenue for the construction of more efficient IR-NLO candidates.

Novel Polytype of III-VI Metal Chalcogenides Nano Crystals Realized in Epitaxially Grown InTe.

III-VI metal chalcogenides have garnered considerable research attention as a novel group of layered van der Waals materials because of their exceptional physical properties and potential technological applications. Here, the epitaxial growth and stacking sequences of InTe is reported, an essential and intriguing material from III-VI metal chalcogenides. Aberration-corrected scanning transmission electron microscopy (STEM) is utilized to directly reveal the interlayer stacking modes and atomic structure, leading to a discussion of a new polytype. Furthermore, correlations between the stacking sequences and interlayer distances are substantiated by atomic-resolution STEM analysis, which offers evidence for strong interlayer coupling of the new polytype. It is proposed that layer-by-layer deposition is responsible for the formation of the unconventional stacking order, which is supported by ab initio density functional theory calculations. The results thus establish molecular beam epitaxy as a viable approach for synthesizing novel polytypes. The experimental validation of the InTe polytype here expands the family of materials in the III-VI metal chalcogenides while suggesting the possibility of new stacking sequences for known materials in this system.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites.

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.

Silicon Chalcogenide Cage Compounds: New Structures Derived from the Bicyclic Silicon(I) Ring Compound Si4 {N(SiMe3 )Mes}4.

The bicyclic silicon(I) ring compound Si4 {N(SiMe3 )Mes}4 (2) was used as starting material in reactions with chalcogens and chalcogen transfer agents at low temperatures. This resulted in the selective formation of new cage compounds. With Me3 NO, a silicon oxide with adamantane-type cage 3 was isolated that represents the first isolated T4 silsesquioxane. Reactions with propylenesulfide and red selenium gave direct access to defect heterocubane-type cages 4 and 5 with three Si-Si bonds wherein the silicon atoms adopt different low oxidation states of +I and +III. A reaction with elemental tellurium even occurs below room temperature to provide ditelluro-tetrasila-tricyclohexane 6.

Two-Dimensional Tetragonal Transition Metal Chalcogenides for High Performance Oxygen Evolution and Reduction: A DFT Study.

The pursuit of high-performance bifunctional catalysts for oxygen evolution/reduction (OER/ORR) has gained significant attention in the field of electrochemical water splitting and fuel cells. In this study, we employed density functional theory (DFT) calculations to investigate a series of 2D tetragonal TMX (TM=transition metal, X=S, Se, Te) monolayers as potential bifunctional electrocatalysts for OER/ORR. To evaluate the overall performance of OER electrocatalysts, we introduced a descriptor, Gmax. The Gmax values obtained for tetragonal CdS, CdSe, FeSe, NiSe, and NiTe monolayers were all below 1.0 V, indicative of their superior catalytic activity and selectivity. Moreover, NiSe displayed remarkable ORR capability with an overpotential (ηORR ) of 0.53 V. Based on the bifunctional index (BI), the catalytic activity ranking for the bifunctional catalysts is as follows: NiSe>NiTe>FeSe>CdS>CdSe>NiS>TiSe>ZnTe. These findings provide an insightful understanding of the electrocatalytic properties of 2D tetragonal TMX monolayers for OER/ORR, opening avenues for the future development of efficient bifunctional electrocatalysts based on 2D tetragonal transition metal chalcogenides.

Recent Developments in Electrodeposition of Transition Metal Chalcogenides-Based Electrode Materials for Advance Supercapacitor Applications: A Review.

High-performance supercapacitive electrode materials have received significant attention from researchers worldwide, thus aiming for comparable performance similar to the extensively used rechargeable batteries. For emerging energy storage technologies like flexible supercapacitors, transition metal chalcogenides (TMCs) have been in the spotlight due to their promising electrochemical features compared to other electrode materials. Among the synthesis techniques, electrodeposition-mediated preparation of thin films of TMCs offered an affordable binder-free approach for electrode fabrication that effectively improved the supercapacitor performance. Hence, this review mainly focussed on the electrodeposition-based syntheses of single/ multinary chalcogenides and their composites for supercapacitors applications. Further, the effects of different deposition parameters were discussed for boosting the supercapacitor performance. Finally, this review outlined the existing challenges and future perspectives in this research domain, which will assist the upcoming exploration in the energy storage field.

Bismuth sulfide micro flowers decorated nickel foam as a promising electrochemical sensor for quantitative analysis of melamine in bottled milk samples.

Here, we demonstrate hydrothermally grown bismuth sulfide (Bi2S3) micro flowers decorated nickel foam (NF) for electrochemical detection of melamine in bottled milk samples. The orthorhombic phase of hydrothermally grown Bi2S3is confirmed by the detailed characterization of x-ray diffraction and its high surface area micro flowers-like morphology is investigated via field emission scanning electron microscope. Furthermore, the surface chemical oxidation state and binding energy of Bi2S3/NF micro flowers is analyzed by x-ray photoelectron spectroscopy studies. The sensor exhibits a wide linear range of detection from 10 ng l-1to 1 mg l-1and a superior sensitivity of 3.4 mA cm-2to melamine using differential pulse voltammetry technique, with a lower limit of detection (7.1 ng l-1). The as-fabricated sensor is highly selective against interfering species of p-phenylenediamine (PPDA), cyanuric acid (CA), aniline, ascorbic acid, glucose (Glu), and calcium ion (Ca2+). Real-time analysis done in milk by the standard addition method shows an excellent recovery percentage of Ì´ 98%. The sensor's electrochemical mechanism studies reveal that the high surface area bismuth sulfide micro flowers surface interacts strongly with melamine molecules through hydrogen bonding and van der Waals forces, resulting in a significant change in the sensor's electrical properties while 3D skeletal Nickel foam as a substrate provides stability, enhances its catalytic activity by providing a more number /of active sites and facilitates rapid electron transfer. The work presented here confirms Bi2S3/NF as a high-performance electrode that can be used for the detection of other biomolecules used in clinical diagnosis and biomedical research.

Electrochemical Sensors Based on Transition Metal Materials for Phenolic Compound Detection.

Electrochemical sensors have been recognized as crucial tools for monitoring comprehensive chemical information, especially in the detection of a significant class of molecules known as phenolic compounds. These compounds can be present in water as hazardous analytes and trace contaminants, as well as in living organisms where they regulate their metabolism. The sensitive detection of phenolic compounds requires highly efficient and cost-effective electrocatalysts to enable the development of high-performance sensors. Therefore, this review focuses on the development of advanced materials with excellent catalytic activity as alternative electrocatalysts to conventional ones, with a specific emphasis on transition metal-based electrocatalysts for the detection of phenolic compounds. This research is particularly relevant in diverse sectors such as water quality, food safety, and healthcare.

General Syntheses of High-Performance Thermoelectric Nanostructured Solids without Post-Synthetic Ligand Stripping.

Ligand-assisted wet chemical synthesis is a versatile methodology to produce controllable nanocrystals (NCs). The post-treatment of ligands is significant for the performance of functional devices. Herein, a method that retains ligands of colloidal-synthesized nanomaterials to produce thermoelectric nanomaterials is proposed, which differs from the conventional methods that strip ligands using multistep cumbersome processes. The ligand-retention method can control the size and dispersity of nanocrystals during the consolidation of the NCs into dense pellets, in which retained ligands are transformed into organic carbon within the inorganic matrices, establishing clear organic-inorganic interfaces. Characterizations of the nonstripped and stripped samples confirm that this strategy can affect electric transport slightly but reduce the thermal conductivity largely. As a result, the materials (e.g., SnSe, Cu2-xS, AgBiSe2, and Cu2ZnSnSe4) with ligands retained achieve higher peak zT and better mechanical properties. This method can be applied to other colloidal thermoelectric NCs and functional materials.

Mn2Ga2S5 and Mn2Al2Se5 van der Waals Chalcogenides: A Source of Atomically Thin Nanomaterials.

Layered chalcogenides containing 3d transition metals are promising for the development of two-dimensional nanomaterials with interesting magnetic properties. Both mechanical and solution-based exfoliation of atomically thin layers is possible due to the low-energy van der Waals bonds. In this paper, we present the synthesis and crystal structures of the Mn2Ga2S5 and Mn2Al2Se5 layered chalcogenides. For Mn2Ga2S5, we report magnetic properties, as well as the exfoliation of nanofilms and nanoscrolls. The synthesis of both polycrystalline phases and single crystals is described, and their chemical stability in air is studied. Crystal structures are probed via powder X-ray diffraction and high-resolution transmission electron microscopy. The new compound Mn2Al2Se5 is isomorphous with Mn2Ga2S5 crystallizing in the Mg2Al2Se5 structure type. The crystal structure is built by the ABCBCA sequence of hexagonal close-packing layers of chalcogen atoms, where Mn2+ and Al3+/Ga3+ species preferentially occupy octahedral and tetrahedral voids, respectively. Mn2Ga2S5 exhibits an antiferromagnetic-like transition at 13 K accompanied by the ferromagnetic hysteresis of magnetization. Significant frustration of the magnetic system may yield spin-glass behavior at low temperatures. The exfoliation of Mn2Ga2S5 layers was performed in a non-polar solvent. Nanolayers and nanoscrolls were observed using high-resolution transmission electron microscopy. Fragments of micron-sized crystallites with a thickness of 70-100 nanometers were deposited on a glass surface, as evidenced by atomic force microscopy.

Cs3In(In4Se7)(P2Se6): A Multi-Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting.

Non-centrosymmetric (NCS) and polar materials capable of exhibiting many important functional properties are indispensable for electro-optical technologies, yet their rational structural design remains a significant challenge. Here, we report a "group grafting" strategy for designing the first multi-chromophore selenophosphate, Cs3In(In4Se7)(P2Se6), that crystallizes in a NCS and polar space group of Cm. The structure features a unique basic building unit (BBU) [In(In4Se10)(P2Se6)], formed through "grafting [In4Se10] supertetrahedra on the root of [In(P2Se6)2] groups". Theoretical calculations confirm that this [In(In4Se10)(P2Se6)] BBU can achieve a "1+1>2" combination of properties from two chromophores, [In4Se10] supertetrahedron and ethane-like [P2Se6] dimer. That makes Cs3In(In4Se7)(P2Se6) exhibit excellent linear and nonlinear optical (NLO) properties, including a strong second harmonic generation (SHG) response (~6×AgGaS2), a large band gap (2.45 eV), broad infrared (IR) transmission (up to 19.5 µm), a significant birefringence (0.26 @1064 nm) as well as the congruently-melting property at ~700 °C. Therefore, Cs3In(In4Se7)(P2Se6) will be a promising NLO crystal, especially in the IR region, and this research also demonstrates that "group grafting" will be an effective strategy for constructing novel polar BBUs with multi-chromophore to design NCS structures and high-performance IR NLO materials.