Asymmetric MoS2 /Graphene/Metal Sandwiches: Preparation, Characterization, and Application

Synergistic Cathode Design for High-Performance Dual-Salt Magnesium/Lithium-Ion Batteries Using 2D/2D 1T/2H-MoS2@Ti3C2Tx MXene Nanocomposite

Magnesium-ion batteries (MIBs) and dual-salt magnesium/lithium-ion batteries (MLIBs) have emerged as promising contenders for next-generation energy storage. In contrast to lithium metal anode in lithium metal batteries, magnesium metal anode in MIBs and MLIBs presents a safer alternative due to the limited dendrite growth and higher volumetric capacity, along with higher natural abundance. This study explores a MLIB configuration with a novel cathode design by employing a 2D/2D nanocomposite of 1T/2H mixed phase MoS2 and delaminated Ti3C2Tx MXene (1T/2H-MoS2@MXene) to address challenges associated with slow kinetics of magnesium ions during cathode interactions. This cathode design takes advantage of the high electrical conductivity of Ti3C2Tx MXene and the expanded interlayer spacing with enhanced conductivity of the 1T metallic phase in 1T/2H mixed phase MoS2. Through a designed synthesis method, the resulting nanocomposite cathode maintains structural integrity, enabling the stable and reversible storage of dual Mg2+ and Li+ ions. The nanocomposite cathode demonstrates superior performance in MLIBs compared to individual components (253 mAh g-1 at 50 mA g-1, and 36% of capacity retention at 1,000 mA g-1), showcasing short ion transport paths and fast ion storage kinetics. This work represents a significant advancement in cathode material design for cost-effective and safe MLIBs.

1T-2H Mixed-Phase MoS2 Stabilized with a Hyperbranched Polyethylene Ionomer for Mg2+ /Li+ Co-Intercalation Toward High-Capacity Dual-Salt Batteries

Dual-salt magnesium/lithium-ion batteries (MLIBs) benefit from fast lithium ion diffusion on the cathode side while providing safety due to the dendrite-free Mg2+ stripping/plating mechanism on the anode side. Bulk MoS2 (B-MoS2 ), as a cathode for magnesium-ion batteries (MIBs), suffers from low conductivity and relatively van der Waals gaps and, consequently, resists against divalent Mg2+ insertion due to the high Coulombic interactions. In MLIBs, it exhibits a Daniell-cell type mechanism with the sole accommodation of Li+ . In this paper, the synthesis of a 1T/2H mixed-phase MoS2 (MP-MoS2 ) modified with a hyperbranched polyethylene ionomer, I@MP-MoS2 , for high-capacity MLIBs with a distinct Mg2+ /Li+ co-intercalation mechanism is reported. Benefiting from the enhanced conductivity (due to 53% metallic 1T phase), expanded van der Waals gaps (79% expansion compared to B-MoS2 , 1.11 vs 0.62 nm), and enhanced interactions with THF-based electrolytes following the modification, I@MP-MoS2 shows a dramatically increased Mg2+ storage compared to its parent analogue (144 mAh g-1 vs ≈2 mAh g-1 at 20 mA g-1 ). In MLIBs, I@MP-MoS2 is demonstrated to exhibit remarkable specific capacities up to ≈270 mAh g-1 at 20 mA g-1 through a Mg2+ /Li+ co-intercalation mechanism with 87% of capacity retention over 200 cycles at 100 mA g-1 .

On the configuration of the graphene/carbon nanotube/graphene van der Waals heterostructure

The graphene/carbon nanotube/graphene (GCG) van der Waals heterostructure is a promising candidate for application in electronics and optical devices, for which the configuration and mechanical properties are of great importance. We perform molecular dynamics simulations to investigate the configuration of the GCG structure, which is successfully interpreted by the mechanic model based on the competition between the bending energy and the adhesion energy. It is found that the cross-section of the nanotube is compressed into an ellipse by the graphene layers, and the eccentricity increases with the increase of the nanotube's diameter. We obtain a concise expression for the relationship between the eccentricity and the nanotube's diameter. These findings shall be valuable for further studies on the physical and mechanical properties of the GCG structure.

Recent Progress on Revealing 3D Structure of Electrocatalysts Using Advanced 3D Electron Tomography: A Mini Review

Electrocatalysis plays a key role in clean energy innovation. In order to design more efficient, durable and selective electrocatalysts, a thorough understanding of the unique link between 3D structures and properties is essential yet challenging. Advanced 3D electron tomography offers an effective approach to reveal 3D structures by transmission electron microscopy. This mini-review summarizes recent progress on revealing 3D structures of electrocatalysts using 3D electron tomography. 3D electron tomography at nanoscale and atomic scale are discussed, respectively, where morphology, composition, porous structure, surface crystallography and atomic distribution can be revealed and correlated to the performance of electrocatalysts. (Quasi) in-situ 3D electron tomography is further discussed with particular focus on its impact on electrocatalysts’ durability investigation and post-treatment. Finally, perspectives on future developments of 3D electron tomography for eletrocatalysis is discussed.

Electrode Materials for Supercapacitors: A Review of Recent Advances

The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors through the development of novel electrode materials. In addition to highlighting the charge storage mechanism of the three main categories of supercapacitors, including the electric double-layer capacitors (EDLCs), pseudocapacitors, and the hybrid supercapacitors, this review describes the insights of the recent electrode materials (including, carbon-based materials, metal oxide/hydroxide-based materials, and conducting polymer-based materials, 2D materials). The nanocomposites offer larger SSA, shorter ion/electron diffusion paths, thus improving the specific capacitance of supercapacitors (SCs). Besides, the incorporation of the redox-active small molecules and bio-derived functional groups displayed a significant effect on the electrochemical properties of electrode materials. These advanced properties provide a vast range of potential for the electrode materials to be utilized in different applications such as in wearable/portable/electronic devices such as all-solid-state supercapacitors, transparent/flexible supercapacitors, and asymmetric hybrid supercapacitors.

Graphene Nanoarchitectonics: Recent Advances in Graphene-Based Electrocatalysts for Hydrogen Evolution Reaction

Under the double pressures of both the energy crisis and environmental pollution, the exploitation and utilization of hydrogen, a clean and renewable power resource, has become an important trend in the development of sustainable energy-production and energy-consumption systems. In this regard, the electrocatalytic hydrogen evolution reaction (HER) provides an efficient and clean pathway for the mass production of hydrogen fuel and has motivated the design and construction of highly active HER electrocatalysts of an acceptable cost. In particular, graphene-based electrocatalysts commonly exhibit an enhanced HER performance owing to their distinctive structural merits, including a large surface area, high electrical conductivity, and good chemical stability. Considering the rapidly growing research enthusiasm for this topic over the last several years, herein, a panoramic review of recent advances in graphene-based electrocatalysts is presented, covering various advanced synthetic strategies, microstructural characterizations, and the applications of such materials in HER electrocatalysis. Lastly, future perspectives on the challenges and opportunities awaiting this emerging field are proposed and discussed.

Simultaneously Engineering Electron Conductivity, Site Density and Intrinsic Activity of MoS2 via the Cation and Anion Codoping Strategy

The catalytic activity of 2H-MoS₂ is retarded by the deficiency in active sites, inferior intrinsic activity, and slow electron transfer kinetics. However, the strategies to concurrently resolve these issues have been challenging and rarely reported. Herein, we successfully endow MoS₂ with exceptional acidic HER performance by concurrently doping nitrogen and metal atoms into the basal plane of MoS₂. The experimental results reveal that the N dopant that induces the intervalence charge transfer between two ions (Mo⁴⁺/Mo³⁺) and the atoms rearrangement can enable the successful synthesis of 1T MoS₂ on reduced graphene oxides, which can concurrently increase the active-site density and facilitate the charge transfer from the substrate to the catalyst active sites. The spontaneous doping of metal cation atoms further improves the intrinsic activity of MoS₂ by creating more sulfur vacancy sites and tailoring the energy level matching. The optimized electrocatalyst exhibited unprecedented activity and stability for HER with a low overpotential of 143 mV at 150 mA cm^-2 and a high exchange current density of 1 mA cm^-2. Therefore, our work opens up possibility to manipulate the MoS₂ catalytic performance to rival Pt, which is of significant importance to both fundamental study and industry applications.

Spinel oxide CoFe2O4 grown on Ni foam as an efficient electrocatalyst for oxygen evolution reaction

The effect of the oxygen evolution reaction (OER) is important in water splitting. In this work, we develop sphere-like morphology spinel oxide CoFe₂O₄/NF by hydrothermal reaction and calcination, and the diameter of the spheres is about 111.1 nm. The CoFe₂O₄/NF catalyst exhibits excellent electrocatalytic performance with an overpotential of 273 mV at a current density of 10 mA cm⁻² and a Tafel slope of 78 mV dec⁻¹. The cycling stability of CoFe₂O₄/NF is remarkable, and it only increased by 5 mV at a current density of 100 mA cm⁻² after 3000 cycles. Therefore, this simple method to prepare CoFe₂O₄/NF can enhance the OER properties of electrocatalysts, which makes CoFe₂O₄/NF a promising material to replace noble metal-based catalysts for the oxygen evolution reaction.

The effect of the oxygen evolution reaction (OER) is important in water splitting.

MoS2/nitrogen doped graphene hydrogels p-n heterojunction: Efficient charge transfer property for highly sensitive and selective photoelectrochemical analysis of chloramphenicol

Constructing junctions between semiconductors is an effective way to promote charge separation and thus to improve the photoelectrochemical (PEC) performances, and specifically, p-n heterojunction is considered as a very promising structure. Herein, we designed and fabricated MoS₂/nitrogen doped graphene hydrogels (MoS₂/NGH) p-n heterojunction by a facile one-pot hydrothermal route. The as-fabricaterd MoS₂/NGH heterostructures demonstrated the excellent PEC activity, exhibiting enhanced photocurrent intensity by the fast transfer and separation rate of photogenerated electron-hole owing to the construction of p-n heterojunction. Based on the high PEC performances of the MoS₂/NGH heterostructure, a novel sensitive PEC sensor was developed for the determination of chloramphenicol (CAP) with the assistance of aptamer. In the presence of target molecules, the as-fabricated PEC sensor could recognize the CAP quickly and then consume the holes in the interface of heterostructures, inhibiting the recombination of photogenerated electron-hole pairs, resulting the enhanced photocurrent. Specially, with the concentration of CAP increased, the photocurrent enhanced gradually. Excellent linearity was obtained in the concentration range from 32.3 ng/L to 96.9 μg/L, and the limit of detection was 3.23 ng/L. Moreover, the as-fabricated PEC sensor exhibited rapid response, high stability, low-cost and high selectivity, which could be successfully applied to the analysis of CAP in honeycomb samples.

Selective Laser-Assisted Synthesis of Tubular van der Waals Heterostructures of Single-Layered PbI2 within Carbon Nanotubes Exhibiting Carrier Photogeneration

The electronic and optical properties of two-dimensional layered materials allow the miniaturization of nanoelectronic and optoelectronic devices in a competitive manner. Even larger opportunities arise when two or more layers of different materials are combined. Here, we report on an ultrafast energy efficient strategy, using laser irradiation, which allows bulk synthesis of crystalline single-layered lead iodide in the cavities of carbon nanotubes by forming cylindrical van der Waals heterostructures. In contrast to the filling of van der Waals solids into carbon nanotubes by conventional thermal annealing, which favors the formation of inorganic nanowires, the present strategy is highly selective toward the growth of monolayers forming lead iodide nanotubes. The irradiated bulk material bearing the nanotubes reveals a decrease of the resistivity as well as a significant increase in the current flow upon illumination. Both effects are attributed to the presence of single-walled lead iodide nanotubes in the cavities of carbon nanotubes, which dominate the properties of the whole matrix. The present study brings in a simple, ultrafast and energy efficient strategy for the tailored synthesis of rolled-up single-layers of lead iodide (i.e., single-walled PbI₂ nanotubes), which we believe could be expanded to other two-dimensional (2D) van der Waals solids. In fact, initial tests with ZnI₂ already reveal the formation of single-walled ZnI₂ nanotubes, thus proving the versatility of the approach.

Synthesis, structure and applications of graphene-based 2D heterostructures

With the profuse amount of two-dimensional (2D) materials discovered and the improvements in their synthesis and handling, the field of 2D heterostructures has gained increased interest in recent years. Such heterostructures not only overcome the inherent limitations of each of the materials, but also allow the realization of novel properties by their proper combination. The physical and mechanical properties of graphene mean it has a prominent place in the area of 2D heterostructures. In this review, we will discuss the evolution and current state in the synthesis and applications of graphene-based 2D heterostructures. In addition to stacked and in-plane heterostructures with other 2D materials and their potential applications, we will also cover heterostructures realized with lower dimensionality materials, along with intercalation in few-layer graphene as a special case of a heterostructure. Finally, graphene heterostructures produced using liquid phase exfoliation techniques and their applications to energy storage will be reviewed.

Janus-Type Gold/Polythiophene Composites Formed via Redox Reaction at the Ionic Liquid|Water Interface

Janus-type Au/polythiophene (PT) composites have been prepared by utilizing the liquid/liquid interface between water (W) and a hydrophobic ionic liquid (IL) as the redox reaction site. AuCl₄^- is reductively deposited, and terthiophene is oxidatively polymerized spacio-selectively at the IL|W interface, leading to the formation of the Au/PT composites. The composites are Janus-type Au-attached PT plates with two surface morphologies, flat surface and flowerlike surface at the W and IL sides of the plates at the IL|W interface, respectively. Not only surface morphologies but also attached Au structures are different at the two surfaces; Au microurchins on the flat surface and dendritic Au nanofibers on the flowerlike surface. Optical and scanning electron microscopic observations have revealed that nanofibers and microurchins are formed at the early and later stage of the reaction, respectively. Electrochemistry at the IL|W interface has illustrated that electron transfer across the IL|W interface during the formation of the Janus-type Au/PT composites is coupled with ion transfer of AuCl₄^- to compensate for the charge unbalance in the two liquid phases. AuCl₄^- transferred into IL is found to be the source of the dendritic Au nanofibers formed at the IL side of the PT plates.

Temperature-dependent Crystallization of MoS2 Nanoflakes on Graphene Nanosheets for Electrocatalysis

This work primarily studies the crystallization condition of molybdenum disulfide (MoS₂) in MoS₂/graphene hybrids by a temperature-varying hydrothermal method from 150 to 240 °C. Flower-like MoS₂ nanoflakes were successfully grown on graphene nanosheets and characterized to understand the temperature-dependent crystallization process and the electrochemical performance. The highest electrocatalytic efficiency for both the dye-sensitized solar cell and the hydrogen evolution reaction was obtained by preparing the hybrid at 180 °C, which benefits from balanced high reactivity and high conductivity. This research leads to a better understanding of temperature dependence of MoS₂ crystallization and offers guidelines for better catalytic material design. Graphical abstract Temperature-dependent Crystallization of MoS₂ Nanoflakes on Graphene Nanosheets for Electrocatalysis.

Capillary-Force-Assisted Clean-Stamp Transfer of Two-Dimensional Materials

A simple and clean method of transferring two-dimensional (2D) materials plays a critical role in the fabrication of 2D electronics, particularly the heterostructure devices based on the artificial vertical stacking of various 2D crystals. Currently, clean transfer techniques rely on sacrificial layers or bulky crystal flakes (e.g., hexagonal boron nitride) to pick up the 2D materials. Here, we develop a capillary-force-assisted clean-stamp technique that uses a thin layer of evaporative liquid (e.g., water) as an instant glue to increase the adhesion energy between 2D crystals and polydimethylsiloxane (PDMS) for the pick-up step. After the liquid evaporates, the adhesion energy decreases, and the 2D crystal can be released. The thin liquid layer is condensed to the PDMS surface from its vapor phase, which ensures the low contamination level on the 2D materials and largely remains their chemical and electrical properties. Using this method, we prepared graphene-based transistors with low charge-neutral concentration (3 × 10¹⁰ cm^-2) and high carrier mobility (up to 48 820 cm² V^-1 s^-1 at room temperature) and heterostructure optoelectronics with high operation speed. Finally, a capillary-force model is developed to explain the experiment.

Solution-processed two-dimensional layered heterostructure thin-film with optimized thermoelectric performance

The content of rGO could alter the carrier transport barrier, and the optimizing power factor was achieved at rGO–MS₂ junctions.