Self-regulating homogenous growth of high-quality graphene on Co-Cu composite substrate for layer control

Graphene-Based Materials for the Separator Functionalization of Lithium-Ion/Metal/Sulfur Batteries

With the escalating demand for electrochemical energy storage, commercial lithium-ion and metal battery systems have been increasingly developed. As an indispensable component of batteries, the separator plays a crucial role in determining their electrochemical performance. Conventional polymer separators have been extensively investigated over the past few decades. Nevertheless, their inadequate mechanical strength, deficient thermal stability, and constrained porosity constitute serious impediments to the development of electric vehicle power batteries and the progress of energy storage devices. Advanced graphene-based materials have emerged as an adaptable solution to these challenges, owing to their exceptional electrical conductivity, large specific surface area, and outstanding mechanical properties. Incorporating advanced graphene-based materials into the separator of lithium-ion and metal batteries has been identified as an effective strategy to overcome the aforementioned issues and enhance the specific capacity, cycle stability, and safety of batteries. This review paper provides an overview of the preparation of advanced graphene-based materials and their applications in lithium-ion, lithium-metal, and lithium-sulfur batteries. It systematically elaborates on the advantages of advanced graphene-based materials as novel separator materials and outlines future research directions in this field.

Rational Design of Binary Alloys for Catalytic Growth of Graphene via Chemical Vapor Deposition

Chemical vapor deposition is the most promising technique for the mass production of high-quality graphene, in which the metal substrate plays a crucial role in the catalytic decomposition of the carbon source, assisting the attachment of the active carbon species, and regulating the structure of the graphene film. Due to some drawbacks of single metal substrates, alloy substrates have gradually attracted attention owing to their complementarity in the catalytic growth of graphene. In this review, we focus on the rational design of binary alloys, such as Cu/Ni, Ni/Mo, and Cu/Si, to control the layer numbers and growth rate of graphene. By analyzing the elementary steps of graphene growth, general principles are summarized in terms of the catalytic activity, metal–carbon interactions, carbon solubility, and mutual miscibility. Several challenges in this field are also put forward to inspire the novel design of alloy catalysts and the synthesis of graphene films bearing desirable properties.

Layer-controlled single-crystalline graphene film with stacking order via Cu-Si alloy formation

Multilayer graphene and its stacking order provide both fundamentally intriguing properties and technological engineering applications. Several approaches to control the stacking order have been demonstrated, but a method of precisely controlling the number of layers with desired stacking sequences is still lacking. Here, we propose an approach for controlling the layer thickness and crystallographic stacking sequence of multilayer graphene films at the wafer scale via Cu-Si alloy formation using direct chemical vapour deposition. C atoms are introduced by tuning the ultra-low-limit CH₄ concentration to form a SiC layer, reaching one to four graphene layers at the wafer scale after Si sublimation. The crystallographic structure of single-crystalline or uniformly oriented bilayer (AB), trilayer (ABA) and tetralayer (ABCA) graphene are determined via nano-angle-resolved photoemission spectroscopy, which agrees with theoretical calculations, Raman spectroscopy and transport measurements. The present study takes a step towards the layer-controlled growth of graphite and other two-dimensional materials.

Boron-doped few-layer graphene nanosheet gas sensor for enhanced ammonia sensing at room temperature

Heteroatom doping in graphene is now a practiced way to alter its electronic and chemical properties to design a highly-efficient gas sensor for practical applications. In this series, here we propose boron-doped few-layer graphene for enhanced ammonia gas sensing, which could be a potential candidate for designing a sensing device. A facile approach has been used for synthesizing boron-doped few-layer graphene (BFLGr) by using a low-pressure chemical vapor deposition (LPCVD) method. Further, Raman spectroscopy has been performed to confirm the formation of graphene and XPS and FESEM characterization were carried out to validate the boron doping in the graphene lattice. To fabricate the gas sensing device, an Si/SiO₂ substrate with gold patterned electrodes was used. More remarkably, the BFLGr-based sensor exhibits an extremely quick response for ammonia gas sensing with fast recovery at ambient conditions. Hence, the obtained results for the BFLGr-based gas sensor provide a new platform to design next-generation lightweight and fast gas sensing devices.

A boron-doped few-layer LPCVD graphene sensor is successfully designed and demonstrated for enhanced NH₃ gas sensing applications.

A review of theoretical study of graphene chemical vapor deposition synthesis on metals: nucleation, growth, and the role of hydrogen and oxygen

Graphene has attracted intense research interest due to its extraordinary properties and great application potential. Various methods have been proposed for the synthesis of graphene, among which chemical vapor deposition has drawn a great deal of attention for synthesizing large-area and high-quality graphene. Theoretical understanding of the synthesis mechanism is crucial for optimizing the experimental design for desired graphene production. In this review, we discuss the three fundamental steps of graphene synthesis in details, i.e. (1) decomposition of carbon feedstocks and formation of various active carbon species, (2) nucleation, and (3) attachment and extension. We provide a complete scenario of graphene synthesis on metal surfaces at atomistic level by means of density functional theory, molecular dynamics (MD), Monte Carlo (MC) and their combination and interface with other simulation methods such as quantum mechanical molecular dynamics, density functional tight binding molecular dynamics, and combination of MD and MC. We also address the latest investigation of the influences of the hydrogen and oxygen on the synthesis and the quality of the synthesized graphene.

Controlled Chemical Synthesis in CVD Graphene

Due to the unique properties of graphene, single layer, bilayer or even few layer graphene peeled off from bulk graphite cannot meet the need of practical applications. Large size graphene with quality comparable to mechanically exfoliated graphene has been synthesized by chemical vapor deposition (CVD). The main development and the key issues in controllable chemical vapor deposition of graphene has been briefly discussed in this chapter. Various strategies for graphene layer number and stacking control, large size single crystal graphene domains on copper, graphene direct growth on dielectric substrates, and doping of graphene have been demonstrated. The methods summarized here will provide guidance on how to synthesize other two-dimensional materials beyond graphene.

Design of catalytic substrates for uniform graphene films: from solid-metal to liquid-metal

The controllable synthesis of uniform graphene with a specific layer number is crucial for both fundamental research and emerging applications due to the high sensitivity of the various extraordinary physicochemical properties of graphene to its layer numbers. However, the excessive segregation of extra C, the inactivation of the self-limiting of Cu and the superabundant nucleation at grain boundaries and defect sites render that the controllable synthesis of uniform graphene is still a challenge. By the employment of various solid and liquid metals with quasi-atomically smooth surfaces to avoid defects or grain boundaries, a series of studies have been performed and significant improvements have been achieved in the controllable synthesis of uniform graphene films. In this review, the representative strategies of designing catalytic substrates, including polycrystalline metals, single-crystalline metals, binary metal alloys and liquid metals, are highlighted. The future of the controllable synthesis of uniform graphene is also discussed.

Two-dimensional heterostructures: fabrication, characterization, and application

Two-dimensional (2D) materials such as graphene, hexagonal boron nitrides (hBN), and transition metal dichalcogenides (TMDs, e.g., MoS2) have attracted considerable attention in the past few years because of their novel properties and versatile potential applications. These 2D layers can be integrated into a monolayer (lateral 2D heterostructure) or a multilayer stack (vertical 2D heterostructure). The resulting artificial 2D structures provide access to new properties and applications beyond their component 2D atomic crystals and hence, they are emerging as a new exciting field of research. In this article, we review recent progress on the fabrication, characterization, and applications of various 2D heterostructures.