Reaction Mechanism and Performance of Innovative 2D Germanane-Silicane Alloys: SixGe1- xH Electrodes in Lithium-Ion Batteries.

The adjustable structures and remarkable physicochemical properties of 2D monoelemental materials, such as silicene and germanene, have attracted significant attention in recent years. They can be transformed into silicane (SiH) and germanane (GeH) through covalent functionalization via hydrogen atom termination. However, synthesizing these materials with a scalable and low-cost fabrication process to achieve high-quality 2D SiH and GeH poses challenges. Herein, groundbreaking 2D SiH and GeH materials with varying compositions, specifically Si0.25Ge0.75H, Si0.50Ge0.50H, and Si0.75Ge0.25H, are prepared through a simple and efficient chemical exfoliation of their Zintl phases. These 2D materials offer significant advantages, including their large surface area, high mechanical flexibility, rapid electron mobility, and defect-rich loose-layered structures. Among these compositions, the Si0.50Ge0.50H electrode demonstrates the highest discharge capacity, reaching up to 1059 mAh g-1 after 60 cycles at a current density of 75 mA g-1. A comprehensive ex-situ electrochemical analysis is conducted to investigate the reaction mechanisms of lithiation/delithiation in Si0.50Ge0.50H. Subsequently, an initial assessment of the c-Li15(SixGe1- x)4 phase after lithiation and the a-Si0.50Ge0.50 phase after delithiation is presented. Hence, this study contributes crucial insights into the (de)lithiation reaction mechanisms within germanane-silicane alloys. Such understanding is pivotal for mastering promising materials that amalgamate the finest properties of silicon and germanium.

Two-Dimensional Van Der Waals Thin Film and Device.

In the rapidly evolving field of thin-film electronics, the emergence of large-area flexible and wearable devices has been a significant milestone. Although organic semiconductor thin films, which can be manufactured through solution processing, have been identified, their utility is often undermined by their poor stability and low carrier mobility under ambient conditions. However, inorganic nanomaterials can be solution-processed and demonstrate outstanding intrinsic properties and structural stability. In particular, a series of two-dimensional (2D) nanosheet/nanoparticle materials have been shown to form stable colloids in their respective solvents. However, the integration of these 2D nanomaterials into continuous large-area thin with precise control of layer thickness and lattice orientation still remains a significant challenge. This review paper undertakes a detailed analysis of van der Waals thin films, derived from 2D materials, in the advancement of thin-film electronics and optoelectronic devices. The superior intrinsic properties and structural stability of inorganic nanomaterials are highlighted, which can be solution-processed and underscor the importance of solution-based processing, establishing it as a cornerstone strategy for scalable electronic and optoelectronic applications. A comprehensive exploration of the challenges and opportunities associated with the utilization of 2D materials for the next generation of thin-film electronics and optoelectronic devices is presented.

Electrochemical Decalcification-Exfoliation of Two-Dimensional Siligene, SixGey: Material Characterization and Perspectives for Lithium-Ion Storage.

A two-dimensional (2D) silicene-germanene alloy, siligene (SixGey), a single-phase material, has attracted increased attention due to its two-elemental low-buckled composition and unique physics and chemistry. This 2D material has the potential to address the challenges caused by low electrical conductivity and the environmental instability of corresponding monolayers. Yet, the siligene structure was studied in theory, demonstrating the material's great electrochemical potential for energy storage applications. The synthesis of free-standing siligene remains challenging and therefore hinders the research and its application. Herein we demonstrate nonaqueous electrochemical exfoliation of a few-layer siligene from a Ca1.0Si1.0Ge1.0 Zintl phase precursor. The procedure was conducted in an oxygen-free environment applying a -3.8 V potential. The obtained siligene exhibits a high quality, high uniformity, and excellent crystallinity; the individual flake is within the micrometer lateral size. The 2D SixGey was further explored as an anode material for lithium-ion storage. Two types of anode have been fabricated and integrated into lithium-ion battery cells, namely, (1) siligene-graphene oxide sponges and (2) siligene-multiwalled carbon nanotubes. The as-fabricated batteries both with/without siligene exhibit similar behavior; however there is an increase in the electrochemical characteristics of SiGe-integrated batteries by 10%. The corresponding batteries exhibit a 1145.0 mAh·g-1 specific capacity at 0.1 A·g-1. The SiGe-integrated batteries demonstrate a very low polarization, confirmed by their good stability after 50 working cycles and a decrease in the solid electrolyte interphase level that occurs after the first discharge/charge cycle. We anticipate the growing potential of emerging two-component 2D materials and their great promise for energy storage and beyond.

InSe:Ge-doped InSe van der Waals heterostructure to enhance photogenerated carrier separation for self-powered photoelectrochemical-type photodetectors.

Two-dimensional (2D) van der Waals (vdW) materials with tunable heterostructures and superior optoelectronic properties have opened a new platform for various applications, e.g., field-effect transistors, ultrasensitive photodetectors and photocatalysts. In this work, an InSe/InSe(Ge) (germanium doped InSe) vdW heterostructure is designed to improve the photoresponse performance of sole InSe in a photoelectrochemical (PEC)-type photodetector. Photoelectrochemical measurements demonstrated that this heterostructure has excellent photoresponse characteristics, including a photocurrent density of 9.8 µA cm-2, a photo-responsivity of 64 µA W-1, and a response time/recovery time of 0.128 s/0.1 s. Moreover, the measurements also revealed the self-powering capability and long-term cycling stability of this heterostructure. The electronic properties of the prepared pure and Ge-doped single crystals unveiled a negative and temperature-independent thermoelectric power and temperature-activated resistivity. The negative character of dominating charge carriers was confirmed by Hall measurements, which corroborated by electrical resistivity revealed a carrier concentration below ∼1015 cm-3 and an electron mobility of ∼500 cm2 V-1 s-1 in Ge-doped crystals. Additionally, the Mott-Schottky model explored the mechanism of charge transfer and enhanced PEC performance. Band bending at the InSe/InSe(Ge)-electrolyte interface benefits the separation and transformation of photogenerated carriers from the heterostructure to electrolyte due to the tunable energy band alignment. These results indicate that the InSe/InSe(Ge) vdW heterostructure is promising for PEC-type photodetectors, which provide a novel way to utilize 2D vdW heterostructures in optoelectronics.

High-Entropy NASICON Phosphates (Na3M2(PO4)3 and NaMPO4Ox, M = Ti, V, Mn, Cr, and Zr) for Sodium Electrochemistry.

High-entropy materials, with complex compositions and unique cocktail characteristics, have recently drawn significant attention. Additionally, a family of sodium super ion conductors (NASICONs)-structured phosphates in energy storage areas shows a comprehensive application for traditional alkaline ion batteries and, in particular, solid-state electrolytes. However, there is no precedent in fabricating this kind of NASICON-type high-entropy phase. Here, we report the successful fabrication of two well-crystallized high-entropy phosphates, namely, Na3(Ti0.2V0.2Mn0.2Cr0.2Zr0.2)2(PO4)3 (HE-N3M2P3) and Na(Ti0.2V0.2Mn0.2Cr0.2Zr0.2)2PO4Ox (HE-NMP). The prepared materials in which the transition metals (TMs) of Ti, V, Mn, Cr, and Zr occupy the same 12c Wykoff position can form a structure analogous to R3̅c Na3V2(PO4)3 that is carefully determined by X-ray diffraction, neutron diffraction, and transmission electron microscopy. Further, their performance for sodium ion batteries and sodium-based solid-state electrolytes was evaluated. The HE-N3M2P3 might exhibit a promising electrochemical performance for sodium storage in terms of its structure resembling that of Na3V2(PO4)3. Meanwhile, the HE-NMP shows considerable electrochemical activity with numerous broad redox ranges during extraction and insertion of Na+, related to the coexistence of several TM elements. The evaluated temperature-dependent ionic conductivity for HE-NMP solid electrolyte varies from 10-6 to 10-5 S cm-1 from room temperature to 398.15 K, offering high potential for energy storage applications as a new high-entropy system.

Edge-Hydrogenated Germanene by Electrochemical Decalcification-Exfoliation of CaGe2: Germanene-Enabled Vapor Sensor.

Two-dimensional germanene has been recently explored for applications in sensing, catalysis, and energy storage. The potential of this van der Waals material lies in its optoelectronic and chemical properties. However, pure free-standing germanene cannot be found in nature, and the synthesis methods are hindering the potentially fascinating properties of germanene. Herein, we report a single-step synthesis of few-layer germanene by electrochemical exfoliation in a nonaqueous environment. As a result of simultaneous decalcification and intercalation of the electrolyte's active ions, we achieved low-level hydrogenation of germanene that occurs at the edges of the material. The obtained edge-hydrogenated germanene flakes have a lateral size of several micrometers and possess a cubic structure. We have pioneered the potential application of edge-hydrogenated germanene for vapor sensing and demonstrated its specific sensitivity to methanol and ethanol. Furthermore, we have shown a selective behavior of the germanene-based sensor that appears to increase the electrical resistance in the vapors where methanol prevails. We anticipate that these results can provide an approach for emerging layered materials with the potential utility in advanced gas sensing.

Multispectral Graphene-Based Electro-Optical Surfaces with Reversible Tunability from Visible to Microwave Wavelengths.

Optical materials with colour-changing abilities have been explored for display devices1, smart windows2,3, or modulation of visual appearance4-6. The efficiency of these materials, however, has strong wavelength dependence, which limits their functionality to a specific spectral range. Here, we report graphene-based electro-optical devices with unprecedented optical tunability covering the entire electromagnetic spectrum from the visible to microwave. We achieve this non-volatile and reversible tunability by electro-intercalation of lithium into graphene layers in an optically accessible device structure. This unique colour-changing capability, together with area-selective intercalation, inspires fabrication of new multispectral devices, including display devices and electro-optical camouflage coating. We anticipate that these results provide realistic approaches for programmable smart optical surfaces with a potential utility in many scientific and engineering fields such as active plasmonics and adaptive thermal management.

The Role of Alkali Cation Intercalates on the Electrochemical Characteristics of Nb2 CTX MXene for Energy Storage.

The intercalation of cations into layered-structure electrode materials has long been studied in depth for energy storage applications. In particular, Li+ -, Na+ -, and K+ -based cation transport in energy storage devices such as batteries and electrochemical capacitors is closely related to the capacitance behavior. We have exploited different sizes of cations from aqueous salt electrolytes intercalating into a layered Nb2 CTx electrode in a supercapacitor for the first time. As a result, we have demonstrated that capacitive performance was dependent on cation intercalation behavior. The interlayer spacing expansion of the electrode material can be observed in Li2 SO4 , Na2 SO4 , and K2 SO4 electrolytes with d-spacing. Additionally, our results showed that the Nb2 CTx electrode exhibited higher electrochemical performance in the presence of Li2 SO4 than in that of Na2 SO4 and K2 SO4 . This is partly because the smaller-sized Li+ transports quickly and intercalates between the layers of Nb2 CTx easily. Poor ion transport in the Na2 SO4 electrolyte limited the electrode capacitance and presented the lowest electrochemical performance, although the cation radius follows Li+ >Na+ >K+ . Our experimental studies provide direct evidence for the intercalation mechanism of Li+ , Na+ , and K+ on the 2D layered Nb2 CTx electrode, which provides a new path for exploring the relationship between intercalated cations and other MXene electrodes.

Self-Powered Broadband Photodetector and Sensor Based on Novel Few-Layered Pd3(PS4)2 Nanosheets.

Optoelectronics and sensing devices are of enormous importance in our modern lives, which has propelled the scientific community to explore new two-dimensional (2D) nanomaterials to meet the requirements of future devices. Herein, we present the exfoliation of palladium thiophosphate (Pd3(PS4)2) by mechanical shear force exfoliation. The Pd3(PS4)2-based photoelectrochemical (PEC) device demonstrated self-powered broadband photodetection in the range of 385-940 nm with an unprecedented responsivity of 2 A W-1 and a specific detectivity of about 8.67 × 1011 cm Hz1/2 W-1 under the illumination of 420 nm LED light. The crucial parameters such as photoresponsivity, response, and recovery time of the device can be controlled by an externally applied voltage and the analyte concentration. Moreover, Pd3(PS4)2-based vapor-sensing devices exhibited frequency-dependent selective acetone sensing in the presence of other organic vapors with an ultrafast response and a recovery time of less than 1 s. Finally, the photocatalytic activity of Pd3(PS4)2 was revealed, which can be attributed to the presence of an appropriate band alignment with the catalytic activity of Pd. This novel material with the aforementioned fascinating phenomenon will pave the way toward practical future applications in optoelectronics and sensing.

Functionalized germanane/SWCNT hybrid films as flexible anodes for lithium-ion batteries.

Germanium, with a high theoretical capacity based on alloyed lithium and germanium (1384 mA h g-1 Li15Ge4), has stimulated tremendous research as a promising candidate anode material for lithium-ion batteries (LIBs). However, due to the alloying reaction of Li/Ge, the problems of inferior cycle life and massive volume expansion of germanium are equally obvious. Among all Ge-based materials, the unique layered 2D germanane (GeH and GeCH3) with a graphene-like structure, obtained by a chemical etching process from the Zintl phase CaGe2, could enable storage of large quantities of lithium between their interlayers. Besides, the layered structure has the merit of buffering the volume expansion due to the tunable interlayer spacing. In this work, the beyond theoretical capacities of 1637 mA h g-1 for GeH and 2048 mA h g-1 for GeCH3 were achieved in the initial lithiation reaction. Unfortunately, the dreadful capacity fading and electrode fracture happened during the subsequent electrochemical process. A solution, i.e. introducing single-wall carbon nanotubes (SWCNTs) into the structure of the electrodes, was found and further confirmed to improve their electrochemical performance. More noteworthy is the GeH/SWCNT flexible electrode, which exhibits a capacity of 1032.0 mA h g-1 at a high current density of 2000 mA g-1 and a remaining capacity of 653.6 mA h g-1 after 100 cycles at 500 mA g-1. After 100 cycles, the hybrid germanane/SWCNT electrodes maintained good integrity without visible fractures. These results indicate that introducing SWCNTs into germanane effectively improves the electrochemical performance and maintains the integrity of the electrodes for LIBs.

Single-Step Synthesis of Platinoid-Decorated Phosphorene: Perspectives for Catalysis, Gas Sensing, and Energy Storage.

The originality of phosphorene is suppressed by its structural defects, irreproducibility, and sensitivity to the ambient environment. To preserve phosphorene's essential characteristics, for example, influencing the charge redistribution and generating the formation of active centers, noble-metal decoration is found to be an efficient approach. Herein, we demonstrate a single-step electrochemical synthesis of platinoid-decorated few-layer phosphorene (FP). The material's structure and effects of metal (Ru, Rh, and Pd) deposition on the FP nanosheets were first explored by numerous analytical techniques and theoretical calculations. Platinoid-decorated FPs demonstrate high quality and consist of one to five layers modified with round- and heptagon-shaped metal nanoparticles with the most intense distribution of Pd. The high-rate Rh deposition provides the enhanced electrocatalytic efficiency for hydrogen evolution (79 mV·dec-1-Tafel slope) and almost 20 times increased capacity for the Li-ion batteries in comparison to bare and Ru-decorated FP. The chemosensing of platinoid-decorated FP indicates a response to methanol plus ethanol and shows inertness to acetone. The incorporation of Ru and Rh nanoparticles increases FP's selectivity toward methanol. This research provides a new approach for the in situ FP functionalization during top-down synthesis and thus broadens the material's feasibility for advanced nanotechnology.

Free-Standing Black Phosphorus Foils for Energy Storage and Catalysis.

Few-layered black phosphorus (BP) is a two-dimensional material that has attracted intensive attention for applications in energy storage and catalysis due to its large surface area and good electrical and thermal conductivity. Herein, a comparable study of BP electrochemical exfoliation in various solutions of tetrabutylammonium salts (TBAX; X is PF6 - , BF4 - , and ClO4 - ) in DMSO is reported. Based on morphological and structural analyses, it is shown that TBAPF6 /DMSO medium was specifically appropriate for the production of high-quality BP nanosheets with micrometer lateral size and a thickness of about 2.4 nm. TBAPF6 /DMSO-processed, few-layered BP exhibits enhanced hydrogen evolution reaction (HER) catalytic activity compared with that of samples exfoliated with the assistance of BF4 - and ClO4 - ions. Finally, the fabrication of flexible, free-standing BP films and their performance in an all-solid-state supercapacitor device are demonstrated.

"Top-down" Arsenene Production by Low-Potential Electrochemical Exfoliation.

Arsenene, as an exotic representative of two-dimensional (2D) materials, has received great interest, yet the interest is mainly based on theoretical study. The reason for this is a restricted ability to operate the material from its synthesis to implementation. Beginning with the production, electrochemical exfoliation has been found as an extremely effective method for the preparation of 2D materials from bulk materials. Here, for the first time, we demonstrate the electrochemical exfoliation of bulk black arsenic in the anhydrous electrolyte medium. Spectro- and microscopic analyses evidence micrometer lateral size few-layer arsenene in a netlike porous shape formed of 2D flakes. We demonstrate that the surfactant-free exfoliation successfully resulted in a stable dispersion for which only washing with the corresponding solvent was sufficient. This electrochemistry route for the black arsenic exfoliation toward few-layer arsenene will broaden the materials' scope applications in new-generation devices.

Non-aqueous solution-processed phosphorene by controlled low-potential electrochemical exfoliation and thin film preparation.

Black phosphorus (BP) in its monolayer form called phosphorene is thought of as a successor of graphene and is of great interest for (opto)electronic applications. A quantitative and scalable method for the synthesis of (mono-)few-layer phosphorene has been an outstanding challenge due to the process irreproducibility and environmental degradation capability of the BP. Here, we report a facile controlled electrochemical exfoliation method for the preparation of a few-layer phosphorene (FP) with nearly 100% yield. Our approach relies on the low-potential influence in anhydrous and oxygen-free low-boiling acetonitrile (AN) and N,N-dimethylformamide (DMF) using alkylammonium ions. Herein, intercalation of positive ions into BP interlayers occurred with a minimum potential of -2.95 V in DMF and -2.85 V in AN and the non-damaging and highly accurate electrochemical exfoliation lasted at -3.8 V. A variety of analytical methods have revealed that in particular DMF-based exfoliation results in high-quality phosphorene of 1-5 layers with good crystallinity and lateral sizes up to tens of micrometers. Moreover, assurance of the oxygen- and water-free environment allowed us to minimize the surface oxidation of BP and, consequently, exfoliated phosphorene. We pioneer an effective and reproducible printing transfer of electrochemically exfoliated phosphorene films onto various flexible and rigid substrates. The surfactant-free process of exfoliation allowed assembly and transfer of thin films based on FP. The phosphorene-based films characterized as direct gap semiconductors have a layer-number-dependent bandgap with a tuning range larger than that of other 2D materials. We show that on varying the films' thickness, it is possible to modify their optical properties, which is a significant advantage for compact and switchable optoelectronic components.

Large-Scale Production of Nanocrystalline Black Phosphorus Ceramics.

Black phosphorus is currently among the most explored two-dimensional (2D) materials. Currently, the synthesis methods are dominantly based on vapor-phase growth of black phosphorus. In this manuscript, we demonstrate large-scale synthesis of black phosphorus by rapid high-pressure transition of red phosphorus. The high-pressure conversion of red phosphorus led to high-density nanocrystalline black phosphorus ceramics. The resulting material was explored in detail including structural and morphological characterization in addition to thermal and electrical transport and basic thermophysical properties. The nanocrystalline black phosphorus can be employed for large-scale production of stable few/single-layer black phosphorus colloidal solutions in various solvents.

Mechanochemical synthesis of carbon-stabilized Cu/C, Co/C and Ni/C nanocomposites with prolonged resistance to oxidation.

Metal-carbon nanocomposites possess attractive physical-chemical properties compared to their macroscopic counterparts. They are important and unique nanosystems with applications including in the future development of nanomaterial enabled sensors, polymer fillers for electromagnetic radiation shields, and catalysts for various chemical reactions. However, synthesis of these nanocomposites typically employs toxic solvents and hazardous precursors, leading to environmental and health concerns. Together with the complexity of the synthetic processes involved, it is clear that a new synthesis route is required. Herein, Cu/C, Ni/C and Co/C nanocomposites were synthesized using a two-step method including mechanochemical treatment of polyethylene glycol and acetates of copper, nickel and cobalt, followed by pyrolysis of the mixtures in an argon flow at 700 °C. Morphological and structural analysis of the synthesized nanocomposites show their core-shell nature with average crystallite sizes of 50 (Cu/C), 18 (Co/C) and 20 nm (Ni/C) respectively. The carbon shell originates from disordered sp2 carbon (5.2-17.2 wt.%) with a low graphitization degree. The stability and prolonged resistance of composites to oxidation in air arise from the complete embedding of the metal core into the carbon shell together with the presence of surface oxide layer of metal nanoparticles. This approach demonstrates an environmentally friendly method of mechanochemistry for controllable synthesis of metal-carbon nanocomposites.

2D WS2 liquid crystals: tunable functionality enabling diverse applications.

The first observation of liquid crystalline dispersions of liquid phase-exfoliated tungsten disulfide flakes is reported in a range of organic solvents. The liquid crystals demonstrate significant birefringence as observed in the linear and circular dichroism measurements respectively. In particular, linear dichroism is observed throughout the visible range while broad-band circular dichroism can be observed in the range from 500-800 nm. Under an applied magnetic field of ±1.5 T the circular dichroism can be switched ON/OFF, while the wavelength range for switching can be tuned from large to narrow range by the proper selection of the host solvent. In combination with photoluminescence capabilities of WS2, this opens a pathway to a wide variety of applications, such as deposition of highly uniform films over large areas for photovoltaic and terahertz devices.

Transmission Properties of FeCl3-Intercalated Graphene and WS2 Thin Films for Terahertz Time-Domain Spectroscopy Applications.

Time-resolved terahertz spectroscopy has become a common method both for fundamental and applied studies focused on improving the quality of human life. However, the issue of finding materials applicable in these systems is still relevant. One of the appropriate solution is 2D materials. Here, we demonstrate the transmission properties of unique graphene-based structures with iron trichloride FeCl3 dopant on glass, sapphire and Kapton polyimide film substrates that previously were not investigated in the framework of the above-described problems in near infrared and THz ranges. We also show properties of a thin tungsten disulfide WS2 film fabricated from liquid crystal solutions transferred to a polyimide and polyethylene terephthalate substrates. The introduction of impurities, the selection of structural dimensions and the use of an appropriate substrate for modified 2D layered materials allow to control the transmission of samples for both the terahertz and infrared ranges, which can be used for creation of effective modulators and components for THz spectroscopy systems.

NLL-Assisted Multilayer Graphene Patterning.

The range of applications of diverse graphene-based devices could be limited by insufficient surface reactivity, unsatisfied shaping, or null energy gap of graphene. Engineering the graphene structure by laser techniques can adjust the transport properties and the surface area of graphene, providing devices of different nature with a higher capacitance. Additionally, the created periodic potential and appearance of the active external/inner/edge surface centers determine the multifunctionality of the graphene surface and corresponding devices. Here, we report on the first implementation of nonlinear laser lithography (NLL) for multilayer graphene (MLG) structuring, which offers a low-cost, single-step, and high-speed nanofabrication process. The NLL relies on the employment of a high repetition rate femtosecond Yb fiber laser that provides generation of highly reproducible, robust, uniform, and periodic nanostructures over a large surface area (1 cm2/15 s). NLL allows one to obtain clearly predesigned patterned graphene structures without fabrication tolerances, which are caused by contacting mask contamination, polymer residuals, and direct laser exposure of the graphene layers. We represent regularly patterned MLG (p-MLG) obtained by the chemical vapor deposition method on an NLL-structured Ni foil. We also demonstrate tuning of chemical (wettability) and electro-optical (transmittance and sheet resistance) properties of p-MLG by laser power adjustments. In conclusion, we show the great promise of fabricated devices, namely, supercapacitors, and Li-ion batteries by using NLL-assisted graphene patterning. Our approach demonstrates a new avenue to pattern graphene for multifunctional device engineering in optics, photonics, and bioelectronics.