Rapid In-Plane Pattern Growth for Large-Area Inverse Replication Through Electrohydrodynamic Instability of Polymer Films.

Nanopatterning driven by electrohydrodynamic (EHD) instability can aid in the resolution of the drawbacks inherent in conventional imprinting or other molding methods. This is because EHD force negates the requirement of physical contact and is easily tuned. However, its potential has not examined owing to the limited size of the pattern replica (several to tens of micrometers). Thus, this study proposes a new route for large-area patterning through high-speed evolution of EHD-driven pattern growth along the in-plane axis. Through the acceleration of the in-plane growth, while selectively controlling a specific edge growth, the pattern replica area can be extended from the micro- to centimeter scale with high fidelity. Moreover, even in the case of nonuniform contact mode, the proposed rapid in-plane growth mode facilitates uniform large-scale replication, which is not possible in conventional imprinting or other molding methods.

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.

Liquid-phase catalyst pre-seeding for controlled growth of layered MoS2 films over a large area via chemical vapor deposition.

We introduce an innovative method that facilitates precise control of high-quality molybdenum disulfide (MoS2) growth, extending up to three layers, on a large scale. This scalable growth is realized by employing solution-based catalysts and precursors in conjunction with chemical vapor deposition (CVD). The catalyst not only diminishes the precursor's activation energy and melting temperature but also augments the overall reaction rate. By regulating the concentration ratio, we directly manipulate the precursor concentrations, thereby promoting clean growth. This unique control mechanism, as delineated in this study, is unprecedented. Our findings confirm that the catalyst introduction does not compromise the quality of the resulting samples. Field effect transistors (FETs) fabricated from the synthesized MoS2 display superior electrical properties; they exhibit a high carrier mobility of 32.1 cm2 V-1 s-1 and an on/off current ratio of 108, signifying their promising electrical performance. Accordingly, our findings suggest that the solution-based CVD strategy presented herein can be potentially utilized for the integration of FETs into a multitude of practical applications.

Electrohydrodynamic Nanopatterning: A Novel Solvent-Assisted Technique for Unconventional Substrates.

Electrohydrodynamic (EHD)-driven patterning is a pioneering lithographic technique capable of replicating and modifying micro/nanostructures efficiently. However, this process is currently restricted to conventional substrates, as it necessitates a uniform and robust electric field over a large area. Consequently, the use of nontraditional substrates, such as those that are flexible, nonflat, or have high insulation, has been notably limited. In our study, we extend the applicability of EHD-driven patterning by introducing a solvent-assisted capillary peel-and-transfer method that allows the successful removal of diverse EHD-induced structures from their original substrates. Compared with the traditional route, our process boasts a success rate close to 100%. The detached structures can then be efficiently transferred to nonconventional substrates, overcoming the limitations of the traditional EHD process. Our method exhibits significant versatility, as evidenced by successful transfer of structures with engineered wettability and patterned structures composed of metals and metal oxides onto nonconventional substrates.

Rapid Electrohydrodynamic-Driven Pattern Replication over a Large Area via Ultrahigh Voltage Pulses.

Despite the prospects of electrohydrodynamic instability patterning (EHIP), poor process parameter controllability is a significant challenge in uniform large-scale nanopatterning. Herein, we introduce a EHIP process using an ultrahigh electric field (>108 V/m) to effectively accelerate the pattern growth evolution. Owing to the strong dependence on a temporal parameter (1/τm) of the field strength, our method not only reduces the completion time of pattern growth but also overcomes critical parametric restrictions on the pattern replication, thereby enhancing the replicated pattern quality in three dimensions. The pattern can be uniformly replicated over the entire film surface even without a perfectly uniform air gap, which has been severely difficult in the conventional method. To further demonstrate how straightforward yet versatile our approach is, we applied our EHIP approach to successfully replicate the densely packed nanostructures of cicada wings.

Transferring 2D TMDs through water-soluble sodium salt catalytic layer.

This study reports a clean and damage-free transfer method that enables the ultrafast transfer of two-dimensional (2D) transition metal dichalcogenides (TMDs) onto desired substrates with a remarkably high yield. We employ a water-soluble sodium salt as both a transfer sacrificial layer for facile transfer and a catalytic layer for the growth of high-quality large-area MoS2using liquid-phase chemical vapor deposition via a catalyzed kinetic growth. We show that the pristine structural and electrical properties of the grown MoS2can be reliably preserved by avoiding detrimental effects during the prolonged harsh-environment transfer process. We demonstrate the technological versatility of the proposed transfer method by fabricating as-transferred MoS2-based back-gated field-effect transistors (FETs). The MoS2FETs exhibit excellent charge mobility as high as 28.7 cm2V-1s-1and an on-off ratio up to ∼107at room temperature, indicating no performance degradation after the transfer process. The proposed transfer method offers universal applicability for various 2D TMDs, mechanical supporting polymers, and target substrates, thus facilitating the facile fabrication of 2D TMD-based electronics and optoelectronics.

High-Performance Flexible Energy Storage Devices Based on Graphene Decorated with Flower-Shaped MoS2 Heterostructures.

MoS2, owing to its advantages of having a sheet-like structure, high electrical conductivity, and benign environmental nature, has emerged as a candidate of choice for electrodes of next-generation supercapacitors. Its widespread use is offset, however, by its low energy density and poor durability. In this study, to overcome these limitations, flower-shaped MoS2/graphene heterostructures have been deployed as electrode materials on flexible substrates. Three-electrode measurements yielded an exceptional capacitance of 853 F g-1 at 1.0 A g-1, while device measurements on an asymmetric supercapacitor yielded 208 F g-1 at 0.5 A g-1 and long-term cyclic durability. Nearly 86.5% of the electrochemical capacitance was retained after 10,000 cycles at 0.5 A g-1. Moreover, a remarkable energy density of 65 Wh kg-1 at a power density of 0.33 kW kg-1 was obtained. Our MoS2/Gr heterostructure composites have great potential for the development of advanced energy storage devices.

Cu2S Nanoflakes Decorated with NiS Nanoneedles for Enhanced Oxygen Evolution Activity.

Metal sulfides are considered excellent materials for oxygen evolution reaction because of their excellent conductivity and high electrocatalytic activity. In this report, the NiS-Cu2S composites were prepared on copper foam (NiS-Cu2S-CF) using a facile synthetic strategy. The scanning electron microscopy results confirmed that the NiS nanoneedles were successfully grown on Cu2S nanoflakes, greatly increasing the active sites. Particularly, the optimized 15% NiS-Cu2S-CF composite demonstrated excellent oxygen evolution activity with a small overpotential of 308 mV@20 mA cm-2, which is significantly smaller than that of noble metal-based electrocatalysts and other NiS-Cu2S-CF composites. The enhanced oxygen evolution activity is attributed to the unique morphology that can provide ample active sites, rich ion-transfer pathways, and the synergistic effect between NiS and Cu2S, which can boost the electron transfer rate.

Interfacial Microenvironment Modulation Enhancing Catalytic Kinetics of Binary Metal Sulfides Heterostructures for Advanced Water Splitting Electrocatalysts.

Interfacial microenvironment modulation has been proven to be a promising route to fabricate highly efficient catalysts. In this work, the lattice defect-rich NiS2 /MoS2 nanoflakes (NMS NFs) electrocatalysts are successfully synthesized by a simple strategy. Benefiting from the abundant lattice defects and modulated interfacial microenvironment between NiS2 and MoS2 , the prepared NMS NFs show superior catalytic activity for water splitting. Particularly, the optimized NMS NFs (the molar ratio of Ni:Mo = 5:5) exhibit remarkable catalytic activity toward overall water splitting with a voltage of 1.60 V at 10 mA cm-2 in alkaline media, which is lower than that of the noble-metal-based electrocatalysts (1.68 V at 10 mA cm-2 ). The NMS NFs electrocatalysts also show exceptional long-term stability (>50 h) for overall water splitting. The density functional theory results demonstrate that the injection of NiS2 into MoS2 can greatly optimize the catalytic kinetics and reduce the energy barrier for hydrogen/oxygen evolution reactions. The work does not only offer a promising candidate for a highly efficient water splitting electrocatalyst but also highlights that interfacial microenvironment modulation is a potential strategy to optimize the catalytic kinetics.

Fog Collection Based on Secondary Electrohydrodynamic-Induced Hybrid Structures with Anisotropic Hydrophilicity.

The outcomes of the study of plant surfaces, such as rice leaves or bamboo leaves, have led to extensive efforts being devoted to fabricating anisotropic arrays of micro/nanoscale features for exploring anisotropic droplet spreading. Nonetheless, precise engineering of the density and continuity of three-phase contact lines for anisotropic wetting remains a significant challenge without resorting to chemical modifications and costly procedures. In this work, we investigated secondary electrohydrodynamic instability in polymer films for producing secondary nanosized patterns between the micrometer-sized grooves by controlling the timescale parameter, 1/τm (>10-4 s-1). We experimentally demonstrated facile morphological control of anisotropic wettability without the use of any chemical modifications. Thus, anisotropic hydrophilic surfaces fabricated by the secondary phase instability of polymer films are advantageous for both droplet condensation and removal, thereby outperforming the water collection efficiency of conventional (isotropic) hydrophilic surfaces in water harvesting applications (∼200 mg·cm-2·h-1) with excellent durability.

Parametric scheme for rapid nanopattern replication via electrohydrodynamic instability.

Electrohydrodynamic (EHD) instability patterning exhibits substantial potential for application as a next-generation lithographic technique; nevertheless, its development continues to be hindered by the lack of process parameter controllability, especially when replicating sub-microscale pattern features. In this paper, a new parametric guide is introduced. It features an expanded range of valid parameters by increasing the pattern growth velocity, thereby facilitating reproducible EHD-driven patterning for perfect nanopattern replication. Compared with conventional EHD-driven patterning, the rapid patterning approach not only shortens the patterning time but also exhibits enhanced scalability for replicating small and geometrically diverse features. Numerical analyses and simulations are performed to elucidate the interplay between the pattern growth velocity, fidelity of the replicated features, and boundary between the domains of suitable and unsuitable parametric conditions in EHD-driven patterning. The developed rapid route facilitates nanopattern replication using EHD instability with a wide range of suitable parameters and further opens up many opportunities for device applications using tailor-made nanostructures in an effective and straightforward manner.

Flexible Supercapacitor-Type Rectifier-free Self-Charging Power Unit Based on a Multifunctional Polyvinylidene Fluoride-ZnO-rGO Piezoelectric Matrix.

The development of an effective mechanical to electrical energy conversion device and its functional integration with an energy storage device for self-powered portable gadgets are cutting-edge research fields. However, the generated power and the mechanical stability of these integrated devices are still not efficient to power up portable electronics. We fabricated a rectifier-free piezoelectric nanogenerator (NG) integrated with a supercapacitor (SC). A multifunctional composite matrix was prepared by the incorporation of ultrathin (<10 nm) ZnO nanoflakes and reduced graphene oxide in polyvinylidene fluoride to enhance the piezoelectric output characteristics and mechanical stability of the device while minimizing the additional energy losses during the integration. The as-fabricated SC-based power unit through the energy conversion and storage processes showed a remarkable self-charging performance. We obtained the maximum output voltage, current density, and power density of about 44 V, 1000 nA cm-2, and 193.6 µW cm-2 under the applied mechanical force of 10 N, respectively. The self-charging behavior of the device showed that it can store 1.5 × 10-3 mC within 100 s without resorting to a rectifier. We obtained the total energy density of about 10.34 mW h kg-1 under palm impact. Our results present a step forward in the development of the NG and SC-based flexible and self-charging devices.

Ice-Templated MXene/Ag-Epoxy Nanocomposites as High-Performance Thermal Management Materials.

High-performance thermal management materials are essential in miniaturized, highly integrated, and high-power modern electronics for heat dissipation. In this context, the large interface thermal resistance (ITR) that occurs between fillers and the organic matrix in polymer-based nanocomposites greatly limits their thermal conductive performance. Herein, through-plane direction aligned three-dimensional (3D) MXene/silver (Ag) aerogels are designed as heat transferring skeletons for epoxy nanocomposites. Ag nanoparticles (NPs) were in situ decorated on exfoliated MXene nanosheets to ensure good contact, and subsequent welding of ice-templated MXene/Ag nanofillers at low temperature of ∼200 °C reduced contact resistance between individual MXene sheets. Monte Carlo simulations suggest that thermal interficial resistance (R0) of the MXene/Ag-epoxy nanocomposite was 4.5 × 10-7 m2 W-1 K-1, which was less than that of the MXene-epoxy nanocomposite (Rc = 5.2 × 10-7 m2 W-1 K-1). Furthermore, a large-scale atomic/molecular massively parallel simulator was employed to calculate the interfacial resistance. It was found that RMXene = 2.4 × 10-9 m2 K W-1, and RMXene-Ag = 2.0 ×10-9 m2 K W-1, respectively, indicating that the Ag NP enhanced the interfacial heat transport. At a relatively low loading of 15.1 vol %, through-plane thermal conductivity reached a value as high as 2.65 W m-1 K-1, which is 1225 % higher than that of pure epoxy resin. Furthermore, MXene/Ag-epoxy nanocomposite film exhibits an impressive thermal conductive property when applied on a Millet 8 and Dell computer for heat dissipation.

Synthesis and Enhanced Photocatalytic Activity of Porous SrTiO3/TiO2 Composites.

Porous photocatalysts have attracted significant attention for their large specific surface area, numerous surface catalytic active sites, and high photocatalytic activity. In this study, porous SrTiO3/TiO2 composites were successfully fabricated through a hydrothermal approach utilizing porous TiO2 as a substrate. The as-synthesized SrTiO3/TiO2 composites were then characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, Brunauer-Emmett-Teller (BET), and ultraviolet-visible spectroscopy (UV-Vis) analysis. The results of SEM and BET indicate that such composites have a porous structure and large surface area. Compared to unadulterated TiO2, SrTiO3 /TiO2 composites exhibit higher photocatalytic performance for the photodegradation of rhodamine B under UV-Vis irradiation. Additionally, it was found that when the content of SrTiO3 reaches 20%, it achieves the maximum photodegradation efficiency of 98.6% under UV-Vis irradiation over 60 min. These results demonstrate that SrTiO3/TiO2 composites are a promising material in terms of environmental cleanliness.

Ultrahigh Output Piezoelectric and Triboelectric Hybrid Nanogenerators Based on ZnO Nanoflakes/Polydimethylsiloxane Composite Films.

We demonstrated a hybrid nanogenerator (NG) exploiting both piezoelectric and triboelectric effects induced from ZnO nanoflakes (NFs)/polydimethylsiloxane (PDMS) composite films through a facile, cost-effective fabrication method. This hybrid NG exhibited not only high piezoelectric output current owing to the enhanced surface piezoelectricity of the ZnO NFs but also high triboelectric output voltage owing to the pronounced triboelectrification of Au-PDMS contact, producing a peak-to-peak output voltage of ∼470 V, a current density of ∼60 µA·cm-2, and an average power density of ∼28.2 mW·cm-2. Without additional energy storage devices, the hybrid NGs with an area of 3 × 3 cm2 instantaneously lit up 180 commercial green light-emitting diodes through periodic hand compression. This approach may provide an innovative design for constructing high-performance and portable energy harvesting devices with enhanced power output, scavenging ambient mechanical energy from human motions in our daily life.

Large-Area High-Quality AB-Stacked Bilayer Graphene on h-BN/Pt Foil by Chemical Vapor Deposition.

Large-area, high-quality bilayer graphene (BLG) has attracted great interest because of its immense potential for many viable applications. However, its growth is still greatly limited owing to its small size and low carrier mobility. In this article, we report the successful growth of large-area, high-quality AB-stacked BLG on hexagonal boron nitride (h-BN)/Pt foil by chemical vapor deposition (CVD). Optical microscopy and scanning electron microscopy observations reveal the formation of uniform and continuous BLG films with sizes of up to 500 µm, which are 4-5 times larger than those reported elsewhere for CVD-grown BLG films. A large carrier mobility of up to 9000 cm2 V-1 s-1 is observed for the BLG films grown on h-BN/Pt foils under ambient conditions. We also propose a plausible growth mechanism of BLG growth on h-BN/Pt foils. Our findings will contribute for the better understanding of the fundamental BLG physics and the development of BLG-based devices.

Poly(dimethylsiloxane)/ZnO Nanoflakes/Three-Dimensional Graphene Heterostructures for High-Performance Flexible Energy Harvesters with Simultaneous Piezoelectric and Triboelectric Generation.

Herein, we report the successful synthesis of poly(dimethylsiloxane)/ZnO nanoflakes/three-dimensional graphene (PDMS/ZnO NFs/3D Gr) heterostructures using Ni foams as the template substrate via a facile route, while adapting a rational material design for a high-performance energy-harvester application. The PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester simultaneously exploits the piezoelectric effect and triboelectrification and shows peak-to-peak output voltages up to 122 V and peak-to-peak current densities up to 51 µA cm-2, resulting in an ultrahigh power density of 6.22 mW cm-2. Furthermore, we have evaluated the performance of the PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester by demonstrating its capacity to instantaneously power up 68 commercially available light-emitting diodes without the need for an additional energy-storage device. The excellent performance of these energy harvesters suggests that PDMS/ZnO NFs/3D Gr heterostructures present a viable strategy for the development of high-performance, flexible, wearable energy-harvesting devices.

Enhanced Power Output of a Triboelectric Nanogenerator using Poly(dimethylsiloxane) Modified with Graphene Oxide and Sodium Dodecyl Sulfate.

In this work, a new approach to modifying poly(dimethylsiloxane) (PDMS) as a negative triboelectric material using graphene oxide (GO) and a sodium dodecyl sulfate (SDS) surfactant was reported. A porous PDMS@GO@SDS composite triboelectric nanogenerator (TENG) could deliver an output voltage and current of up to 438 V and 11 µA/cm2, respectively. These values were 3-fold higher than those of the flat PDMS. The superior performance is attributed to the intensified negative charges on PDMS from the oxygen functional groups of GO and anionic head groups of the SDS molecules. The outstanding performance and straightforward, low-cost fabrication process of the PDMS@GO@SDS TENG would be beneficial for the further development of powerful NGs integrated into wearable electronics and self-charging power cells.