Mengqi Zeng

Supercritical Carbon Dioxide Anchored Fe3O4 Nanoparticles on Graphene Foam and Lithium Battery Performance

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.

Direct Growth of Ultrafast Transparent Single‐Layer Graphene Defoggers

The idea flat surface, superb thermal conductivity and excellent optical transmittance of single-layer graphene promise tremendous potential for graphene as a material for transparent defoggers. However, the resistance of defoggers made from conventional transferred graphene increases sharply once both sides of the film are covered by water molecules which, in turn, leads to a temperature drop that is inefficient for fog removal. Here, the direct growth of large-area and continuous graphene films on quartz is reported, and the first practical single-layer graphene defogger is fabricated. The advantages of this single-layer graphene defogger lie in its ultrafast defogging time for relatively low input voltages and excellent defogging robustness. It can completely remove fog within 6 s when supplied a safe voltage of 32 V. No visible changes in the full defogging time after 50 defogging cycles are observed. This outstanding performance is attributed to the strong interaction forces between the graphene films and the substrates, which prevents the permeation of water molecules. These directly grown transparent graphene defoggers are expected to have excellent prospects in various applications such as anti-fog glasses, auto window and mirror defogging.

Emerging two-dimensional nanomaterials for electrochemical hydrogen evolution

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.

High-mobility graphene on liquid p-block elements by ultra-low-loss CVD growth

The high-quality and low-cost of the graphene preparation method decide whether graphene is put into the applications finally. Enormous efforts have been devoted to understand and optimize the CVD process of graphene over various d-block transition metals (e.g. Cu, Ni and Pt). Here we report the growth of uniform high-quality single-layer, single-crystalline graphene flakes and their continuous films over p-block elements (e.g. Ga) liquid films using ambient-pressure chemical vapor deposition. The graphene shows high crystalline quality with electron mobility reaching levels as high as 7400 cm2 V−1s−1 under ambient conditions. Our employed growth strategy is ultra-low-loss. Only trace amounts of Ga are consumed in the production and transfer of the graphene and expensive film deposition or vacuum systems are not needed. We believe that our research will open up new territory in the field of graphene growth and thus promote its practical application.

Direct growth of molybdenum disulfide on arbitrary insulating surfaces by chemical vapor deposition

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.

Self-Assembly of Graphene Single Crystals with Uniform Size and Orientation: The First 2D Super-Ordered Structure

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.

Li-storage performance of binder-free and flexible iron fluoride@graphene cathodes

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.

Exploring Two-Dimensional Materials toward the Next-Generation Circuits: From Monomer Design to Assembly Control

Two-dimensional (2D) materials have attracted tremendous research interest since the breakthrough of graphene. Their unique optical, electronic, and mechanical properties hold great potential for harnessing them as key components in novel applications for electronics and optoelectronics. Their atomic thickness and exposed huge surface even make them highly designable and manipulable, leading to the extensive application potentials. Whats more, after acquiring the qualification for being the candidate for next-generation devices, the assembly of 2D materials monomers into mass or ordered structure is also of great importance, which will determine their ultimate industrialization. By designing the monomers and regulating their assembling behavior, the exploration of 2D materials toward the next-generation circuits can be spectacularly achieved. In this review, we will first overview the emerging 2D materials and then offer a clear guideline of varied physical and chemical strategies for tuning their properties. Furthermore, assembly strategies of 2D materials will also be included. Finally, challenges and outlooks in this promising field are featured on the basis of its current progress.

Isotropic Growth of Graphene toward Smoothing Stitching.

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.

Controllable Sliding Transfer of Wafer‐Size Graphene

The innovative design of sliding transfer based on a liquid substrate can succinctly transfer high‐quality, wafer‐size, and contamination‐free graphene within a few seconds. Moreover, it can be extended to transfer other 2D materials. The efficient sliding transfer approach can obtain high‐quality and large‐area graphene for fundamental research and industrial applications.