仲云雷

Aggregated suspensions of 2D materials with high-enough concentrations can be processed into homogenous gel inks for various printing and coating methods. The stability of the inks, their rheological properties, and film formation behavior mainly depend on their interflake van der Waals interactions, eliminating the need for addition of the conventional additives and enabling their room-temperature processing.

Abstract

Processing 2D materials into printable or coatable inks for the fabrication of functional devices has proven to be quite difficult. Additives are often used in large concentrations to address the processing challenges, but they drastically degrade the electronic properties of the materials. To remove the additives a high-temperature post-deposition treatment can be used, but this complicates the fabrication process and limits the choice of materials (i.e., no heat-sensitive materials). In this work, by exploiting the unique properties of 2D materials, a universal strategy for the formulation of additive-free inks is developed, in which the roles of the additives are taken over by van der Waals (vdW) interactions. In this new class of inks, which is termed “vdW inks”, solvents are dispersed within the interconnected network of 2D materials, minimizing the dispersibility-related limitations on solvent selection. Furthermore, flow behavior of the inks and mechanical properties of the resultant films are mainly controlled by the interflake vdW attractions. The structure of the vdW inks, their rheological properties, and film-formation behavior are discussed in detail. Large-scale production and formulation of the vdW inks for major high-throughput printing and coating methods, as well as their application for room-temperature fabrication of functional films/devices are demonstrated.

Although studied for decades, 2D materials have often struggled to surpass small scales. Recent progress in the larger-scale synthesis of graphene represents an exciting paradigm shift. An overview of scalable graphene powder and film production is provided, addressing industrial and academic trends, and specifically highlighting flash Joule heating methods.

Abstract

In the past 17 years, the larger-scale production of graphene and graphene family materials has proven difficult and costly, thus slowing wider-scale commercial applications. The quality of the graphene that is prepared on larger scales has often been poor, demonstrating a need for improved quality controls. Here, current industrial graphene synthetic and analytical methods, as well as recent academic advancements in larger-scale or sustainable synthesis of graphene, defined here as weights more than 200 mg or films larger than 200 cm², are compiled and reviewed. There is a specific emphasis on recent research in the use of flash Joule heating as a rapid, efficient, and scalable method to produce graphene and other 2D nanomaterials. Reactor design, synthetic strategies, safety considerations, feedstock selection, Raman spectroscopy, and future outlooks for flash Joule heating syntheses are presented. To conclude, the remaining challenges and opportunities in the larger-scale synthesis of graphene and a perspective on the broader use of flash Joule heating for larger-scale 2D materials synthesis are discussed.

2D all-inorganic NbWO₆ perovskite nanosheets with thicknesses down to 1.5 nm are synthesized for the fabrication of gas sensors, and the fabricated few-layer NbWO₆-based semiconducting sensor exhibits fast H₂S sensing speed with high selectivity and sensitivity at low temperature.

Abstract

Hydrogen sulfide (H₂S) detection with high selectivity and low working temperature is of great significance due to its strong toxicity both to the environment and to humans and also as an endogenous signaling molecule existing in various physiological processes. 2D perovskites with high carrier mobility are promising candidates for gas sensing; however, the development of stable and nontoxic 2D perovskites nanosheets still remains a challenge. Herein, 2D all-inorganic NbWO₆ perovskite nanosheets with thicknesses down to 1.5 nm are synthesized by liquid exfoliation, and the gas-sensing performance based on these ultrathin nanosheets is investigated. A few-layer NbWO₆-based sensor exhibits fast H₂S sensing speed (<6 s) with high selectivity and sensitivity (S = 12.5 vs 50 ppm) at low temperature (150 °C). A small variation of H₂S concentration (<0.5 ppm) can be detected with a fully reversible resistance signal. This work sheds light on the development of high-performance gas sensors working in ambient conditions based on low-dimensional, nontoxic, and wide-bandgap perovskite semiconductors. The high carrier mobility, ultrathin structure, and soft nature make this type of 2D perovskite semiconductor an ideal material candidate for the fabrication of flexible, transparent, and wearable sensing devices in the future.

Author(s): Shenyang Huang, Yang Lu, Fanjie Wang, Yuchen Lei, Chaoyu Song, Jiasheng Zhang, Qiaoxia Xing, Chong Wang, Yuangang Xie, Lei Mu, Guowei Zhang, Hao Yan, Bin Chen, and Hugen Yan

Through infrared spectroscopy, we systematically study the pressure effect on electronic structures of few-layer black phosphorus (BP) with layer number ranging from 2 to 13. We reveal that the pressure-induced shift of optical transitions exhibits strong layer dependence. In sharp contrast to the b...

[Phys. Rev. Lett. 127, 186401] Published Tue Oct 26, 2021

A joint experiment-theory investigation is conducted to unveil the fracture mechanics of grain boundaries (GBs) in low-symmetry monolayer rhenium disulfide at the single-atom level. GBs having different Re chain alignment with respect to the GB orientation display disparate crack behaviors, indicating the GB type-dependent mechanical failure in anisotropic 2D polycrystals, which gives fundamental insights into GB engineering.

Abstract

Grain boundaries (GBs) play a central role in the fracture of polycrystals. However, the complexity of GBs and the difficulty in monitoring the atomic structure evolution during fracture greatly limit the understanding of the GB mechanics. Here, in situ aberration-corrected scanning transmission electron microscopy and density functional theory calculations are combined to investigate the fracture mechanics in low-symmetry, polycrystalline, 2D rhenium disulfide (ReS₂), unveiling the distinctive crack behaviors at different GBs with atomic resolution. Brittle intergranular fracture prefers to rip through the GBs that are parallel to the Re chains of at least one side of the GBs. In contrast, those GBs, which do not align with Re chains on either side of the GBs, are highly resistant to fracture, impeding or deflecting the crack propagation. These results disclose the GB type-dependent mechanical failure of anisotropic 2D polycrystals, providing new ideas for material reinforcement and controllable cutting via GB engineering.

Research progress for elemental 2D materials in the areas of synthesis, properties, and applications in catalytic nitrogen reduction for electrochemical ammonia synthesis is examined systematically. The major challenges in the solution-processed synthesis of elemental 2D materials and their use for electrochemical ammonia synthesis are discussed.

Abstract

Graphene and related elemental 2D materials have become core materials in nanotechnology and shown great promise for industrially important electrocatalysis reactions. Although excellent progress has been made over the past few years, research into the field of elemental 2D materials beyond graphene is still at an early stage. Importantly, recent research has revealed the promising efficacy of elemental 2D materials as effective nitrogen reduction reaction (NRR) electrocatalysts due to their many excellent properties including high surface activities, acting as active sites for effective functionalization and defect engineering. This review provides a comprehensive account of recent advances in elemental 2D materials with a major focus on the solution-based synthesis routes and their applications in electrocatalytic NRR for ammonia (NH₃) production. After a concise overview of elemental 2D materials, the advantages and challenges of currently available methods for the synthesis of these 2D materials are discussed. Then, the review focuses on the use of these emerging 2D materials in the electrocatalytic reduction of N₂ for sustainable (NH₃) synthesis. Finally, the challenges still to be addressed, and important perspectives in this attractive field are emphasized.

Lithium encapsulation and its confined growth kinetics in amorphous carbon nanotubes (aCNTs) are studied using in situ transmission electron microscopy. The carbon shells play dual roles, providing geometric/mechanical constraints and electron/ion transport channels, which profoundly alter the Li growth patterns, resulting in unusual Li nanostructures. Importantly, it is revealed that sufficient nitrogen/oxygen doping is critical for aCNTs to reliably encapsulate lithium.

Abstract

Encapsulation of lithium in the confined spaces within individual nanocapsules is intriguing and highly desirable for developing high-performance Li metal anodes. This work aims for a mechanistic understanding of Li encapsulation and its confined growth kinetics inside 1D enclosed spaces. To achieve this, amorphous carbon nanotubes are employed as a model host using in situ transmission electron microscopy. The carbon shells have dual roles, providing geometric/mechanical constraints and electron/ion transport channels, which profoundly alter the Li growth patterns. Li growth/dissolution takes place via atom addition/removal at the free surfaces through Li⁺ diffusion along the shells in the electric field direction, resulting in the formation of unusual Li structures, such as poly-crystalline nanowires and free-standing 2D ultrathin (1–2 nm) Li membranes. Such confined front-growth processes are dominated by Li {110} or {200} growing faces, distinct from the root growth of single-crystal Li dendrites outside the nanotubes. Controlled experiments show that high lithiophilicity/permeability, enabled by sufficient nitrogen/oxygen doping or pre-lithiation, is critical for the stable encapsulation of lithium inside carbonaceous nanocapsules. First-principles-based calculations reveal that N/O doping can reduce the diffusion barrier for Li⁺ penetration, and facilitate Li filling driven by energy minimization associated with the formation of low-energy Li/C interfaces.

2D amorphous MoS₃-on-rGO heterostructure is constructed via an isotropic growth process for beyond-lithium-ion batteries (Na⁺, K⁺, and Zn²⁺) with outstanding electrochemical performance and superior cyclic stability. The amorphous MoS₃-on-rGO exhibits low strain and fast reaction kinetics during cycling.

Abstract

Beyond-lithium-ion storage devices are promising alternatives to lithium-ion storage devices for low-cost and large-scale applications. Nowadays, the most of high-capacity electrodes are crystal materials. However, these crystal materials with intrinsic anisotropy feature generally suffer from lattice strain and structure pulverization during the electrochemical process. Herein, a 2D heterostructure of amorphous molybdenum sulfide (MoS₃) on reduced graphene surface (denoted as MoS₃-on-rGO), which exhibits low strain and fast reaction kinetics for beyond-lithium-ions (Na⁺, K⁺, Zn²⁺) storage is demonstrated. Benefiting from the low volume expansion and small sodiation strain of the MoS₃-on-rGO, it displays ultralong cycling performance of 40 000 cycles at 10 A g⁻¹ for sodium-ion batteries. Furthermore, the as-constructed 2D heterostructure also delivers superior electrochemical performance when used in Na⁺ full batteries, solid-state sodium batteries, K⁺ batteries, Zn²⁺ batteries and hybrid supercapacitors, demonstrating its excellent application prospect.

h-BN is one of the most promising inorganic materials of this century, with possible applications ranging from aerospace to medicine. It has emerged as an exotic 2D material in the post-graphene era, owing to its exciting optoelectrical properties combined with mechanical robustness, thermal stability, and chemical inertness. An encyclopedic view of the structure, properties, synthesis, and applications of h-BN is provided.

Abstract

Hexagonal boron nitride (h-BN) has emerged as a strong candidate for two-dimensional (2D) material owing to its exciting optoelectrical properties combined with mechanical robustness, thermal stability, and chemical inertness. Super-thin h-BN layers have gained significant attention from the scientific community for many applications, including nanoelectronics, photonics, biomedical, anti-corrosion, and catalysis, among others. This review provides a systematic elaboration of the structural, electrical, mechanical, optical, and thermal properties of h-BN followed by a comprehensive account of state-of-the-art synthesis strategies for 2D h-BN, including chemical exfoliation, chemical, and physical vapor deposition, and other methods that have been successfully developed in recent years. It further elaborates a wide variety of processing routes developed for doping, substitution, functionalization, and combination with other materials to form heterostructures. Based on the extraordinary properties and thermal-mechanical-chemical stability of 2D h-BN, various potential applications of these structures are described.

Stable doping by modulating the thickness is realized in 2D layered materials. The decreasing thickness-induced lattice deformation makes defects in PtSSe transit from Pt vacancies in thicker PtSSe to anion vacancies in thinner PtSSe, which leads to controllable doping. Thickness-modulated doping shows great potential in novel electronics and optoelectronics, especially including diodes and photodetectors.

Abstract

For each generation of semiconductors, the issue of doping techniques is always placed at the top of the priority list since it determines whether a material can be used in the electronic and optoelectronic industry or not. When it comes to 2D materials, significant challenges have been found in controllably doping 2D semiconductors into p- or n-type, let alone developing a continuous control of this process. Here, a unique self-modulated doping characteristic in 2D layered materials such as PtSSe, PtS_0.8Se_1.2, PdSe₂, and WSe₂ is reported. The varying number of vertically stacked-monolayers is the critical factor for controllably tuning the same material from p-type to intrinsic, and to n-type doping. Importantly, it is found that the thickness-induced lattice deformation makes defects in PtSSe transit from Pt vacancies to anion vacancies based on dynamic and thermodynamic analyses, which leads to p- and n-type conductance, respectively. By thickness-modulated doping, WSe₂ diode exhibits a high rectification ratio of 4400 and a large open-circuit voltage of 0.38 V. Meanwhile, the PtSSe detector overcomes the shortcoming of large dark-current in narrow-bandgap optoelectronic devices. All these findings provide a brand-new perspective for fundamental scientific studies and applications.

High-capacity, stable, and flexible lithium–metal composite yarns (LMCYs) are realized via the fast and scalable capillary filling, a nonreactive wetting process without the use of lithium-reactive materials. The use of LMCYs as anodes endows wire-type lithium–metal batteries with a high energy density of ≈293 Wh L⁻¹, a long cyclic life over 800 cycles, and good foldability.

Abstract

High-capacity and omnidirectionally flexible wire-type lithium (Li)–metal batteries represent a feasible technology for the realization of electronic textiles. However, the use of commercially available Li–metal wires as anodes nowadays confronts many electrochemical and mechanical issues such as dendrite formation, low yield strength, and poor fatigue resistance. Here, a flexible and stable Li–metal composite yarn (LMCY) is designed via a fast capillary filling of molten Li into metallic carbon yarn for fabricating high-energy-density and long-lasting wire-type Li–metal batteries. LMCY shows outstanding electrochemical cyclic stability, mechanical strength, flexibility, and durability. Pairing lithium–iron phosphate (LFP) with the LMCY as anode results in a foldable LFP||Li full cell that delivers a high energy density over 290 Wh L⁻¹ and a long lifetime over 800 cycles with a capacity retention of over 50% after 750 charge/discharge cycles. The seamless integration of this wire-shape LFP||Li cell with commercial textiles is demonstrated as a built-in power supply to wearable electronics, while maintaining the excellent breathability of the textiles. LMCYs are also adaptable to other high-performance wire-type batteries, such as lithium–sulfur battery.

Nature Communications, Published online: 24 September 2021; doi:10.1038/s41467-021-25922-8

Author(s): Zhehao Ge, Sergey Slizovskiy, Frédéric Joucken, Eberth A. Quezada, Takashi Taniguchi, Kenji Watanabe, Vladimir I. Fal’ko, and Jairo Velasco, Jr.

Bloch states of electrons in honeycomb two-dimensional crystals with multivalley band structure and broken inversion symmetry have orbital magnetic moments of a topological nature. In crystals with two degenerate valleys, a perpendicular magnetic field lifts the valley degeneracy via a Zeeman effect...

[Phys. Rev. Lett. 127, 136402] Published Thu Sep 23, 2021

An ionogel with tailorable mechanical properties is prepared by a facile one-step polymerization and used as a water-resistant electrode. The hydrophobic polymer networks inside the ionogel endow this ionogel with excellent stability, adhesion, and self-healing ability underwater. Compared to commercial gel electrodes, this ionogel electrode can collect real-time electrocardiography signals in an aquatic environment.

Abstract

Underwater electrocardiography (ECG) monitoring, which can monitor cardiac autonomic changes and arrhythmias during diving, is essential for sports management and healthcare. However, it is crucial yet rather challenging to achieve ECG monitoring in an aquatic environment because the interface electrodes may lose their functionality underwater. Here, an ionogel with tailorable mechanical properties is prepared by a facile one-step polymerization and used as water-resistant electrode. The Young's modulus and strain at break of the ionogel can be modulated in the range of 0.22–337 MPa and 349 to >10 000%, respectively. The hydrophobic polymer networks inside the ionogel endow this ionogel with excellent stability, adhesion, and self-healing ability underwater. The ionic conductivity imparted by the free ionic groups inside the ionogel allows the ionogel to detect and transmit physiological electrical signals. Compared with commercial gel electrodes, this ionogel electrode demonstrates better adhesion ability, conductivity, and stability underwater. The ionogel electrode can collect real-time ECG signals effectively both in the air and underwater, and the data can be used to warn users of the potential risk of a heart attack.