The synthesis and integration of core–shell materials have been extensively explored in three-dimensional nanostructures, while they are hardly ever extended into the emerging two-dimensional (2D) research field. Herein, demonstrated by graphene (G) and hexagonal boron nitride (h-BN) and via a sequential chemical vapor deposition method, we succeed for the first time in synthesizing 2D h-BN–G core–shell arrays (CSA), which possess extremely high uniformity in shapes, sizes and distributions. Each of the core–shell units is composed of G ring-shaped shell internally filled with h-BN circular core. In addition, we perform simulations to further explain the self-symmetrical etching growth mechanism of the h-BN–G CSA, demonstrating its potential to be used as an efficient synthetic method suitable for other 2D CSA systems.

Monolayer transition metal dichalcogenides (TMDs) possess great potential in the electronic and optoelectronic devices on account of their unique electronic structure as well as outstanding characteristics. However, presented growth approaches are hardly to avoid multilayers and the root cause of this thermodynamic growth process lies on the overflowing transition metal sources. Here, a novel substrate-trapping strategy (STS) is developed to achieve monolayer TMDs crystals over the whole substrate surface. A designed substrate with appropriate reaction activity to fix the extra precursors is the key, for which the dominance of the dynamics will be established, thus leading to strict self-limited monolayer growth behavior. The high-quality nature of the synthesized monolayer MoS2 crystals is also clarified by transmission electron microscopy characterizations and field-effect transistors performance. Excellent tolerance to variations in growth parameters of STS is therefore exhibited and, moreover, it is also verified in achieving strictly monolayer WS2 crystals, thus demonstrating the universality of this approach. The facile strategy opens up a new avenue in growth of monolayer TMDs and may facilitate their industrial applications.

Hydrogen has been verified as a clean and economical energy source, due to its high mass energy density and renewability. Electrochemical water splitting is regarded as one of the most economical and eco-friendly approaches for hydrogen evolution. Recently, emerging two-dimensional (2D) nanomaterials have demonstrated their potential as distinguished non-noble catalysts for hydrogen evolution. These ultrathin nanomaterials are dramatically different from their bulk counterparts. Abundant active sites are maximally exposed and the small diffusion paths of the ultrathin nanosheets can effectively facilitate charge transfer in the electrocatalytic hydrogen evolution. Moreover, many tactics can be easily adopted in such an interesting and adjustable platform, which makes the 2D material an ideal object to explore the exciting catalytic activity and electronic transfer. Various inventive strategies regarding increasing active sites, improving intrinsic activity and enhancing electrical conductivity for enhancing catalytic performance are urgently pursued. Here, the primary criteria for evaluating catalysts in electrochemical HER is discussed, followed by a brief introduction of the superiorities of 2D nanomaterial catalysts for HER. Based on these, recent strategies for improving the catalytic activity of 2D nanomaterials are summarized. We believe this review will provide deep insights for understanding the 2D material catalysts for catalyzing HER, and aid in devising new catalysts with high catalytic activity.

The 2D atomic structure and fascinating properties of graphene provide new opportunities for the surface-functionalization of the traditional structural materials to meet the demands for intelligent and informational applications. Conformal coating of graphene in any arbitrary-shape, even 3D irregular shapes, is critical to the surface-functionalized structural materials in their actual form for practical applications. Herein, as demonstrated by ceramics, this study successfully obtains graphene conformal-coated ceramics via rationally designed a compatible strategy with the fabrication of traditional ceramics. The graphene films show intimate adherence on the arbitrary-shaped ceramics and exhibit uniform distribution even on the concave and convex surfaces. With a practical scalability, the present work stimulates various applications of heating devices, electroluminescent devices, and touchpads in real-life scenarios.

•The synthesis processes of 2D materials for bioelectronics devices were detailed.•Macrostructures composed by 2D materials showed great potentials in biosensing.•Five typical bioelectronics devices based on 2D materials were overviewed.•2D material bioelectronics devices have been applied in all aspects of biosensing.In recent years, graphene and related two-dimensional (2D) materials have emerged as exotic materials in nearly every fields of fundamental science and applied engineering. The latest progress has shown that these 2D materials could have a profound impact on bioelectronics devices. For the construction of these bioelectronics devices, these 2D materials were generally synthesized by the processes of exfoliation and chemical vapor deposition. In particular, the macrostructures of these 2D materials have also been realized by these two processes, which have shown great potentials in the self-supported and special-purpose biosensors. Due to the high specific surface area, subtle electron properties, abundant surface atoms of these 2D materials, the as-constructed bioelectronics devices have exhibited enhanced performance in the sensing of small biomolecules, heavy metals, pH, protein and DNA. The aim of this review article is to provide a comprehensive scientific progress in the synthesis of 2D materials for the construction of five typical bioelectronics devices (electrochemical biosensors, FET-based biosensors, piezoelectric devices, electrochemiluminescence devices and supercapacitors) and to overview the present status and future perspective of the applications of these bioelectronics devices based on 2D materials.

As a member of the group IVB transition metal dichalcogenides (TMDs) family, hafnium disulfide (HfS2) is recently predicted to exhibit higher carrier mobility and higher tunneling current density than group VIB (Mo and W) TMDs. However, the synthesis of high-quality HfS2 crystals, sparsely reported, has greatly hindered the development of this new field. Here, a facile strategy for controlled synthesis of high-quality atomic layered HfS2 crystals by van der Waals epitaxy is reported. Density functional theory calculations are applied to elucidate the systematic epitaxial growth process of the S-edge and Hf-edge. Impressively, the HfS2 back-gate field-effect transistors display a competitive mobility of 7.6 cm2 V−1 s−1 and an ultrahigh on/off ratio exceeding 108. Meanwhile, ultrasensitive near-infrared phototransistors based on the HfS2 crystals (indirect bandgap ≈1.45 eV) exhibit an ultrahigh responsivity exceeding 3.08 × 105 A W−1, which is 109-fold higher than 9 × 10−5 A W−1 obtained from the multilayer MoS2 in near-infrared photodetection. Moreover, an ultrahigh photogain exceeding 4.72 × 105 and an ultrahigh detectivity exceeding 4.01 × 1012 Jones, superior to the vast majority of the reported 2D-materials-based phototransistors, imply a great promise in TMD-based 2D electronic and optoelectronic applications.

The self-assembly of two-dimensional (2D) nanomaterials, an emerging research area, still remains largely unexplored. The strong interlayer attraction between 2D nanosheets leads to face-to-face stacking rather than edge-to-edge coupling. We demonstrate, for the first time, how one can induce and control an edge-to-edge self-assembly process for 2D nanomaterials. The extremely weak van der Waals coupling and strong anisotropy of ReS2 allow us to realize an oriented self-assembly (OSA) process. The aspect ratio of the resulting ReS2 nanoscrolls can be well controlled. In addition, we perform simulations to further explain and confirm the OSA process, demonstrating its great potential to be expanded as a general edge-to-edge self-assembly process suitable for other 2D nanomaterials.

The challenges facing the rapid developments of highly integrated electronics, photonics, and microelectromechanical systems suggest that effective fabrication technologies are urgently needed to produce ordered structures using components with high performance potential. Inspired by the spontaneous organization of molecular units into ordered structures by noncovalent interactions, we succeed for the first time in synthesizing a two-dimensional superordered structure (2DSOS). As demonstrated by graphene, the 2DSOS was prepared via self-assembly of high-quality graphene single crystals under mutual electrostatic force between the adjacent crystals assisted by airflow-induced hydrodynamic forces at the liquid metal surface. The as-obtained 2DSOS exhibits tunable periodicity in the crystal space and outstanding uniformity in size and orientation. Moreover, the intrinsic property of each building block is preserved. With simplicity, scalability, and continuously adjustable feature size, the presented approach may open new territory for the precise assembly of 2D atomic crystals and facilitate its application in structurally derived integrated systems.

Inspired by pinecone, here we develop a novel kind of direct chemical vapour deposition (CVD) derived graphene-encapsulated porous Si nanoparticles (NPs) on graphene foam (GF). The CVD derived graphene sheets on the surface of Si NPs are partly overlapped, act as the squamae of a pinecone, preventing the direct exposure to the electrolyte. When the Si NPs expand, a sliding between the graphene layers occurs, providing an effective way to accommodate the volume expansion and stabilize the solid electrolyte interphase. As a result, the pinecone-like graphene-encapsulated Si electrodes exhibit a high capacity of 1600 mA h g−1 at a current density of 2100 mA g−1 after 300 cycles and a capacity higher than 800 mA h g−1 at a current density of 8400 mA g−1.

Conversion reaction electrode materials (CREMs) have gained significant interest in lithium-ion batteries (LIBs) owing to their high theoretical gravimetric capacity. However, traditional CREMs-based electrodes, with large strain arising from Li+ intercalation/deintercalation causes pulverization or electrical breakdown and cracking of the active materials which leads to structural collapse, limiting performance. Therefore, in order to construct electrodes with a strong tolerance to the strain incurred during the conversion reaction process, we design a coral-like three-dimensional (3D) hierarchical heterostructure by using cross-linked nanoflakes interspersed with nanoparticles (NPs) standing vertically on graphene foam (GF). The coral-like 3D hierarchical heterostructures can efficiently disperse the strain from both internal and external forces as well as increase the specific surface area for enhanced electrochemical reactions. These features lead to long-cycle stability and excellent flexibility in LIBs. Fe3O4 NPs and CoO NFs are utilized as a model system to demonstrate our strategy. The as-prepared coral-like hierarchical electrode is studied as an anode in LIBs for the first time and is shown to deliver a high reversible specific gravimetric capacity of ∼1200 mA h g–1 at a rate of 0.5 A g–1 for 400 cycles. In addition, our batteries can even power a green light-emitting diode when bent to high degrees confirming the excellent flexibility of the material.Keywords: coral-like; flexible; lithium-ion battery anode; long cycle; strain dispersion

Liquid metal, such as Ga, has been demonstrated to be a good catalyst to grow uniform graphene at about 1000 °C. However, at reduced temperature, the high surface tension of Ga causes the limited spreading-ability over the supporting substrate, which prevents the formation of large-area graphene. Here we present that the addition of Cu could efficiently decrease the surface tension of Ga, thus achieving a larger coverage. We succeeded in growing large-area, uniform and single-layer graphene at 800 °C by atmospheric chemical vapour deposition using CH4 as the carbon source.

Newborn two-dimensional materials (NB2DMs) beyond graphene such as transition metal dichalcogenides (TMDs) exhibit excellent optoelectronic and mechanical properties as well as high theoretical specific capacity, which make them become the promising building blocks of flexible energy devices related to energy conversion and storage. Compared to graphene with zero band gap or traditional friable materials such as Si, these NB2DMs are more suitable to construct flexible devices as active layers of optoelectronic devices or as active materials for batteries. The present review focuses on the recent advances in bendable energy devices based on NB2DMs, including batteries, supercapacitors (SCs), solar cells, photodetectors and nanogenerators (NGs). The NB2DMs pave a new way to construct next-generation flexible energy devices with improved performance and we believe that those devices will be seen in our daily life and change our lifestyle in the immediate future.近年来, 智能可穿戴电子产品开始走入我们的日常生活, 同时也极大地激发了研究者们对柔性能源的研究兴趣. 以过渡金属二硫族 化合物为代表的新兴二维材料表现出了优秀的光电和机械性能、高的理论比容量等性质, 使其在柔性能源存储和转换领域备受关注. 相 比于零带隙且比容量低的石墨烯或者硅等传统材料, 这些新兴的二维材料在构筑柔性光电器件及二次电池方面具有良好的应用前景. 本 文综述了新型二维材料在二次电池、超级电容器、太阳能电池、光电探测器和纳米发电机等柔性能源应用领域的突破性进展. 虽然目前 这个新兴领域仍面临众多问题, 但是通过结构与材料的设计与优化, 有望在不久的将来逐步得到解决. 我们相信这些新兴二维材料的应用 将显著提高柔性能源器件的性能, 并推动可穿戴电子产品在我们日常生活中的普及.

Improved properties arise in transition metal dichalcogenide (TMDC) materials when they are stacked onto insulating hexagonal boron nitride (h-BN). Therefore, the scalable fabrication of TMDCs/h-BN heterostructures by direct chemical vapor deposition (CVD) growth is highly desirable. Unfortunately, to achieve this experimentally is challenging. Ideal substrates for h-BN growth, such as Ni, become sulfides during the synthesis process. This leads to the decomposition of the pregrown h-BN film, and thus no TMDCs/h-BN heterostructure forms. Here, we report a thoroughly direct CVD approach to obtain TMDCs/h-BN vertical heterostructures without any intermediate transfer steps. This is attributed to the use of a nickel-based alloy with excellent sulfide-resistant properties and a high catalytic activity for h-BN growth. The strategy enables the direct growth of single-crystal MoS2 grains of up to 200 μm2 on h-BN, which is approximately 1 order of magnitude larger than that in previous reports. The direct band gap of our grown single-layer MoS2 on h-BN is 1.85 eV, which is quite close to that for free-standing exfoliated equivalents. This strategy is not limited to MoS2-based heterostructures and so allows the fabrication of a variety of TMDCs/h-BN heterostructures, suggesting the technique has promise for nanoelectronics and optoelectronic applications.Keywords: direct CVD growth; MoS2/h-BN heterostructures; optical properties; sulfide-resistant alloy;

The quality of graphene grown via chemical vapor deposition still has very great disparity with its theoretical property due to the inevitable formation of grain boundaries. The design of single-crystal substrate with an anisotropic twofold symmetry for the unidirectional alignment of graphene seeds would be a promising way for eliminating the grain boundaries at the wafer scale. However, such a delicate process will be easily terminated by the obstruction of defects or impurities. Here we investigated the isotropic growth behavior of graphene single crystals via melting the growth substrate to obtain an amorphous isotropic surface, which will not offer any specific grain orientation induction or preponderant growth rate toward a certain direction in the graphene growth process. The as-obtained graphene grains are isotropically round with mixed edges that exhibit high activity. The orientation of adjacent grains can be easily self-adjusted to smoothly match each other over a liquid catalyst with facile atom delocalization due to the low rotation steric hindrance of the isotropic grains, thus achieving the smoothing stitching of the adjacent graphene. Therefore, the adverse effects of grain boundaries will be eliminated and the excellent transport performance of graphene will be more guaranteed. What is more, such an isotropic growth mode can be extended to other types of layered nanomaterials such as hexagonal boron nitride and transition metal chalcogenides for obtaining large-size intrinsic film with low defect.Keywords: graphene; isotropic growth; liquid metal; smooth stitching

It has been generally accepted that iron-group metals (iron, cobalt, nickel) consistently show the highest catalytic activity for the growth of carbon nanomaterials, including carbon nanotubes (CNTs) and graphene. However, it still remains a challenge for them to obtain uniform graphene, because of their high carbon solubility, which can be attributed to an uncontrollable precipitation in cooling process. The quality and uniformity of the graphene grown on low-cost iron-group metals determine whether graphene can be put into the mass productions or not. Here, we develop a novel strategy to form an antiperovskite layer using ambient-pressure chemical vapor deposition (APCVD), which, so far, is the only known way for iron-group metals to prepare uniform monolayer graphene with 100% surface coverage. Our strategy utilizes liquid metal (e.g., gallium) to assist iron-group metals to form an antiperovskite layer that is chemically stable throughout the high-temperature growth process and then to seal the passageway of carbon segregation from the metal bulk during cooling. With the advantage of forming antiperovskite structure, the uniform monolayer graphene can always be obtained under the variations of experimental conditions. Our strategy solves the problem about how to get uniform graphene film on high-solubility carbon substrate, to utilize the high catalytic activity of low-cost iron-group metals and to realize low-temperature growth by chemical vapor deposition.

As flexible devices have become increasingly popular in our daily life, flexible energy-supply devices, especially flexible lithium-ion batteries (LIBs), have attracted great attention. Graphene foam is a lightweight, flexible and conductive interconnected network that can be directly used as a current collector material to disperse active materials. FeF3·0.33H2O is a suitable active cathode material with a high theoretical capacity and natural abundance. But its poor ionic and electrical conductivity limits its application. In order to combine the superior qualities of GF and FeF3·0.33H2O, we developed a scCO2-assisted method to grow FeF3·0.33H2O flower-like arrays perpendicularly on GF. Consequently, the designed composites efficiently combine the good flexibility of GF and high energy storage capacity of FeF3·0.33H2O. The strong interaction between GF and FeF3·0.33H2O established by the scCO2 method greatly improves the electron transport and ion migration. Thus, the obtained flexible electrode requires no binder, metal current collectors and conducting agents. It shows a capacity of about 145 mA h g−1 at a current density of 1C (200 mA g−1) after assembled as a cathode electrode.

Host–guest interactions, especially those between cyclodextrins (CDs, including α-, β- and γ-CD) and various guest molecules, exhibit a very high supramolecular recognition ability. Thus, they have received considerable attention in different fields. These specific interactions between host and guest molecules are promising for biosensing and clinical detection. However, there is a lack of an ideal electrode substrate for CDs to increase their performance in electrochemical sensing. Herein, we propose a new 3D nitrogen-doped graphene (3D-NG) based electrochemical sensor, taking advantage of the superior sensitivity of host–guest interactions. Our 3D-NG was fabricated by a template-directed chemical vapour deposition (CVD) method, and it showed a large specific surface area, a high capacity for biomolecules and a high electron transfer efficiency. Thus, for the first time, we took 3D-NG as an electrode substrate for β-CD to establish a new type of biosensor. Using dopamine (DA) and acetaminophen (APAP) as representative guest molecules, our 3D-NG/β-CD biosensor shows extremely high sensitivities (5468.6 μA mM−1 cm−2 and 2419.2 μA mM−1 cm−2, respectively), which are significantly higher than those reported in most previous studies. The stable adsorption of β-CD on 3D-NG indicates potential applications in clinical detection and medical testing.

In recent years, graphene-based enzyme biosensors have received considerable attention due to their excellent performance. Enormous efforts have been made to utilize graphene oxide and its derivatives as carriers of enzymes for biosensing. However, the performance of these sensors is limited by the drawbacks of graphene oxide such as slow electron transfer rate, low catalytic area and poor conductivity. Here, we report a new graphene-based enzyme carrier, i.e. a highly conductive 3D nitrogen-doped graphene structure (3D-NG) grown by chemical vapour deposition, for highly effective enzyme-based biosensors. Owing to the high conductivity, large porosity and tunable nitrogen-doping ratio, this kind of graphene framework shows outstanding electrical properties and a large surface area for enzyme loading and biocatalytic reactions. Using glucose oxidase (GOx) as a model enzyme and chitosan (CS) as an efficient molecular binder of the enzyme, our 3D-NG based biosensors show extremely high sensitivity for the sensing of glucose (226.24 μA mM−1 m−2), which is almost an order of magnitude higher than those reported in most of the previous studies. The stable adsorption and outstanding direct electrochemical behaviour of the enzyme on the nanocomposite indicate the promising application of this 3D enzyme carrier in high-performance electrochemical biosensors or biofuel cells.

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.

Manganese dioxide (MnO2) is a promising anode material because of its high theoretical capacity, environmental friendliness and abundant natural reserves. However, its application in lithium ion batteries is still hindered by rapid capacity fading and low rate performance resulting from large volume expansion and low conductivity. We construct a stable structure with ultrathin interconnected MnO2 nanoflakes (NFs) assembled on the chemical vapor deposition (CVD) grown graphene foam (GF) via a facile hydrothermal process. Without the use of any binder, conductive additives or any other current collector, the designed electrode benefits from shorter transport path, larger electrode/electrolyte contact area, more stable structure to buffer volume expansion during cycling. As a result, the composites show increased cycle life and deliver a high capacity of about 1200 mAh g−1 at the current density of 500 mA g−1 after 300 cycles and a capacity higher than 500 mAh g−1 at a current density of 5 A g−1.

We report a direct growth approach of large area, uniform and patternable few layer molybdenum disulfide on arbitrary insulating substrates, including polymers and glass. The method can effectively control the number of layers with 100% surface coverage and avoid the transferring process.

The self-limited chemical vapor deposition of uniform single-layer graphene on Cu foils generated significant interest when it was initially discovered. Soon after, the fabrication of real uniform graphene was found to need extremely precise control of the growth conditions. Slight deviations terminate the self-limiting homogeneous growth, inevitably leading to multilayer graphene formation. Here we propose an innovative way to utilize liquid metals to resolve this thorny problem. In stark contrast to the low carbon solubility found in solid metals (e.g., Cu), catalytically decomposed carbon atoms are embedded in liquid metals. During cooling, the homogeneous solidified surface forms from the quasi-atomic smooth liquid surface, and carbon precipitation is blocked by the frozen metal lattices, which are insoluble to carbon. The underlying liquid bulk acts as a container to buffer the excess carbon supply, which normally would lead to the formation of multilayer graphene in the conventional CVD process. As a result, the growth of graphene becomes governed by a self-limiting surface catalytic process and is robust to variations in growth conditions. With simplicity, scalability, and a large growth window, the use of liquid metals provides an attractive solution to obtain uniform graphene.

Magnetite (Fe3O4) is an attractive electrode material due to its high theoretical capacity, eco-friendliness, and natural abundance. However, its commercial application in lithium-ion batteries is still hindered by its poor cycling stability and low rate capacity resulting from large volume expansion and low conductivity. We present a new approach which makes use of supercritical carbon dioxide to efficiently anchor Fe3O4 nanoparticles (NPs) on graphene foam (GF), which was obtained by chemical vapor deposition in a single step. Without the use of any surfactants, we obtain moderately spaced Fe3O4 NPs arrays on the surface of GF. The particle size of the Fe3O4 NPs exhibits a narrow distribution (11 ± 4 nm in diameter). As a result, the composites deliver a high capacity of about 1200 mAh g–1 up to 500 cycles at 1 C (924 mAh g–1) and about 300 mAh g–1 at 20 C, which reaches a record high using Fe3O4 as anode material for lithium-ion batteries.Keywords: Fe3O4 nanoparticles; graphene foam; lithium-ion battery; supercritical CO2

This paper describes preparation and characterization of electrochemically functional graphene nanostructure incorporating adsorption of electroactive methylene blue (MB) dye onto graphene and nanocomposite assembled using layer-by-layer of graphene with MB on solid substrates. UV–visible spectroscopy, FT-IR spectroscopy, Raman spectroscopy and electrochemistry for systematical characterization of the MB adsorption onto graphene reveal the formation of a MB/graphene adsorptive nanostructure through π–π stacking and hydrophobic interactions. Compared with MB adsorbed onto a graphene oxide (GO) modified electrode and MB adsorbed onto a GC electrode, MB adsorbed onto a graphene modified electrode exhibits a good stability and distinct electrochemical properties. Additionally, MB adsorbed onto graphene can improve the water-disperse ability of graphene. Furthermore, scanning electron microscopy, UV–vis-NIR spectroscopy and electrochemistry demonstrated that directly layer-by-layer assembling of MB and graphene was an excellent route to prepare a functional nanocomposite on different solid substrates including silica plate, quartz slide and glassy carbon electrode. The excellent electroactivity and the high stability of electrochemically functional graphene nanostructure and the layered nanocomposite are envisaged to make them very useful electrochemically functional nanomaterials for practical development of electronic devices such as biosensors and photovoltaic cells.

•A novel liquid metal solvent based co-segregation (LMSCS) strategy was employed to directly fabricate 2D WC single crystals embedded in graphene film, i.e. a unique in-plane heterostructure, over a large scale in one step via chemical vapor deposition (CVD).•This 2D in-plane WC–graphene heterostructure (i-WC–G) was firstly applied in HER. Basing on the high crystallinity of the WC and utilizing the interfacial synergistic catalytic effects, the 2D i-WC–G heterostructure exhibited excellent electrocatalytic activity for the HER.•The overpotential was as low as 120 mV and the Tafel slope was 38 mV/decade, which indicated higher performance and efficiency than mainstream 2D HER catalysts.•The reproducible polarization plot even after 5000 voltammetry (CV) cycles highlighted the excellent durability of our developed 2D i-WC–G heterostructure.•Such a versatile synthesis approach will allow the fabrication of other high-quality 2D transition metal carbides (TMCs) and their embedding in in-plane structures and this will promote the practical catalytic application of metal carbides.Electrochemical water splitting is regarded as one of the most economical and eco-friendly approaches for hydrogen revolution. Developing a low-cost and earth-abundant non-noble-metal catalyst will be of the most significance. Tungsten carbide (WC) is highly promising due to its platinum (Pt) -like behavior in surface catalysis. Here we first report a liquid metal solvent based co-segregation (LMSCS) strategy to fabricate a high uniformity of 2D WC crystals embedded in graphene by chemical vapor deposition (CVD) in one step. The 2D in-plane WC–graphene heterostructures (i-WC–G) are remarkably stable under an electro-catalytic environment and ensure good interfacial synergy between the 2D WC crystallites and graphene to achieve a more effective hydrogen evolution. The overpotential is as low as 120 mV and the Tafel slope is 38 mV/dec, which indeed exhibits outstanding catalytic potential among the reported 2D material systems. Our elegant and versatile approach allows the fabrication of other high-quality 2D transition metal carbides (TMCs) and their in-plane heterostructures, which will further promote practical catalytic applications of metal carbides.A liquid metal solvent based co-segregation strategy was proposed to fabricate a high uniformity of 2D WC crystals embedded in the few-layer graphene by chemical vapor deposition (CVD) in one step. In addition, the efficient catalytic ability of the 2D WC for the hydrogen evolution, for the first time, was experimentally exhibited.

Inspired by pinecone, here we develop a novel kind of direct chemical vapour deposition (CVD) derived graphene-encapsulated porous Si nanoparticles (NPs) on graphene foam (GF). The CVD derived graphene sheets on the surface of Si NPs are partly overlapped, act as the squamae of a pinecone, preventing the direct exposure to the electrolyte. When the Si NPs expand, a sliding between the graphene layers occurs, providing an effective way to accommodate the volume expansion and stabilize the solid electrolyte interphase. As a result, the pinecone-like graphene-encapsulated Si electrodes exhibit a high capacity of 1600 mA h g−1 at a current density of 2100 mA g−1 after 300 cycles and a capacity higher than 800 mA h g−1 at a current density of 8400 mA g−1.

As flexible devices have become increasingly popular in our daily life, flexible energy-supply devices, especially flexible lithium-ion batteries (LIBs), have attracted great attention. Graphene foam is a lightweight, flexible and conductive interconnected network that can be directly used as a current collector material to disperse active materials. FeF3·0.33H2O is a suitable active cathode material with a high theoretical capacity and natural abundance. But its poor ionic and electrical conductivity limits its application. In order to combine the superior qualities of GF and FeF3·0.33H2O, we developed a scCO2-assisted method to grow FeF3·0.33H2O flower-like arrays perpendicularly on GF. Consequently, the designed composites efficiently combine the good flexibility of GF and high energy storage capacity of FeF3·0.33H2O. The strong interaction between GF and FeF3·0.33H2O established by the scCO2 method greatly improves the electron transport and ion migration. Thus, the obtained flexible electrode requires no binder, metal current collectors and conducting agents. It shows a capacity of about 145 mA h g−1 at a current density of 1C (200 mA g−1) after assembled as a cathode electrode.

Hydrogen has been verified as a clean and economical energy source, due to its high mass energy density and renewability. Electrochemical water splitting is regarded as one of the most economical and eco-friendly approaches for hydrogen evolution. Recently, emerging two-dimensional (2D) nanomaterials have demonstrated their potential as distinguished non-noble catalysts for hydrogen evolution. These ultrathin nanomaterials are dramatically different from their bulk counterparts. Abundant active sites are maximally exposed and the small diffusion paths of the ultrathin nanosheets can effectively facilitate charge transfer in the electrocatalytic hydrogen evolution. Moreover, many tactics can be easily adopted in such an interesting and adjustable platform, which makes the 2D material an ideal object to explore the exciting catalytic activity and electronic transfer. Various inventive strategies regarding increasing active sites, improving intrinsic activity and enhancing electrical conductivity for enhancing catalytic performance are urgently pursued. Here, the primary criteria for evaluating catalysts in electrochemical HER is discussed, followed by a brief introduction of the superiorities of 2D nanomaterial catalysts for HER. Based on these, recent strategies for improving the catalytic activity of 2D nanomaterials are summarized. We believe this review will provide deep insights for understanding the 2D material catalysts for catalyzing HER, and aid in devising new catalysts with high catalytic activity.