Liang Mei

Bio: Liang Mei is an academic researcher from City University of Hong Kong. The author has contributed to research in topics: Electron transfer & Exfoliation joint. The author has an hindex of 4, co-authored 7 publications receiving 65 citations.

Intercalation and exfoliation chemistries of transition metal dichalcogenides

Abstract: Large-scale preparation of single-layer transition metal dichalcogenides (TMDs) is significant due to their potential applications, such as catalysis, electronics, energy storage and conversion. In order to meet the application requirements, TMD nanosheets need to be mass-produced with a high yield, uniform size, and good quality. Several strategies have been developed to prepare 2D TMDs, such as mechanical exfoliation, chemical vapor deposition, and liquid exfoliation. Liquid exfoliation, which can be categorized into direct exfoliation and intercalation-based exfoliation, is a promising method since it can be employed for mass production, structural modification, and fabrication of 2D TMD composites. Intercalation can expand the interlayer spacing, weaken the van der Waals force, and change the structure of the host materials. Exfoliation can break the van der Waals force between the adjacent layers by exerting certain external strengths. However, the detailed mechanisms of both intercalation and exfoliation are not clear; this limits their potential applications. This review aims to provide a comprehensive summary about the intercalation and exfoliation processes of layered materials as well as their properties and applications. Our main attention is the underlying reaction mechanism during chemical or electrochemical intercalation in addition to the exfoliation process. The applications of 2D TMDs fabricated from exfoliation are also introduced in this review. In the last part, we provide some perspectives on the fundamental research and practical applications of TMDs.

A Safe Flexible Self-Powered Wristband System by Integrating Defective MnO2-x Nanosheet-Based Zinc-Ion Batteries with Perovskite Solar Cells.

Abstract: The booming market of portable and wearable electronics has aroused the requests for advanced flexible self-powered energy systems featuring both excellent performance and high safety. Herein, we report a safe, flexible, self-powered wristband system by integrating high-performance zinc-ion batteries (ZIBs) with perovskite solar cells (PSCs). ZIBs were first fabricated on the basis of a defective MnO2-x nanosheet-grown carbon cloth (MnO2-x@CC), which was obtained via the simple lithium treatment of the MnO2 nanosheets to slightly expand the interlayer spacing and generate rich oxygen vacancies. When used as a ZIB cathode, the MnO2-x@CC with a ultrahigh mass loading (up to 25.5 mg cm-2) exhibits a much enhanced specific capacity (3.63 mAh cm-2 at current density of 3.93 mA cm-2), rate performance, and long cycle stability (no obvious degradation after 5000 cycles) than those of the MnO2@CC. Importantly, the MnO2-x@CC-based quasi-solid-state ZIB not only achieves excellent flexibility and an ultrahigh energy density of 5.11 mWh cm-2 (59.42 mWh cm-3) but also presents a high safety under a wide temperature range and various severe conditions. More importantly, the flexible ZIBs can be integrated with flexible PSCs to construct a safe, self-powered wristband, which is able to harvest light energy and power a commercial smart bracelet. This work sheds light on the development of high-performance ZIB cathodes and thus offers a good strategy to construct wearable self-powered energy systems for wearable electronics.

Impact of electron transfer of atomic metals on adjacent graphyne layers on electrochemical water splitting.

Abstract: Efficient electrocatalysts are needed for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), while the influence of electron transfer from the adjacent layer of multilayered electrocatalysts on their catalytic performance is usually neglected. Here, we used the single cobalt atom trapped graphyne catalyst (Co@GY) to study the feasibility of modulating its water-splitting catalytic activity through interfacial electron transfer. A series of Co@GY/transition-metal doped graphyne double-layered structures (Co@GY/GY and Co@GY/TM@GY, TM = Mn, Fe, Co, Ni, Cu) are systematically evaluated for water splitting via theoretical computations. The electronic structure analyses of different stacking cases revealed that the atomic metals on the adjacent TM@GY layer remarkably tune the electronic structures of the Co atom in the Co@GY layer. A strong linear correlation between ΔGH* and the d band center of the Co atom was found, suggesting that the HER activity on the Co atom can be tailored by adjusting the TM on the adjacent TM@GY layer with different d-electron occupations. The volcano-type trend of OER catalytic performance is obtained to show the best Co@GY/Ni@GY catalyst for the OER with an over-potential of 0.38 V, indicating that higher catalytic performance arises from moderate interfacial electron transfer. These results arouse a re-thinking of the intrinsic activity origins of single-atom catalysts (SACs) and offer a new strategy for the structure designing of SACs.

Advanced materials and technologies for supercapacitors used in energy conversion and storage: a review

Abstract: Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.

Strategies on regulating Zn2+ solvation structure for dendrites-free and side reactions-suppressed zinc-ion batteries

Abstract: High‐safety and low‐cost aqueous zinc‐ion batteries (ZIBs) are an exceptionally compelling technology for grid‐scale energy storage, whereas the corrosion, hydrogen evolution reaction and dendrites growth of Zn anodes plague their...

Surface phonon dispersion of MoS2

Abstract: : The dispersion of phonons on the (0001) surface of MoS2 was measured by high-resolution electron energy loss spectroscopy along both the and azimuths (i.e., r to K and r to M respectively). The surface phonons have lower energies than the corresponding bulk phonons, which indicates that the bonding interactions of the surface atoms are different from those of the bulk, even in a layer lattice compound. Since sputtered MOS2 lubricant films are composed of many small crystallites, the relative number of surface atoms in a film is much higher than in a single crystal. The stronger bonding of the surface layer may affect the amount of inter- vs intra-crystalline slip in the lubrication mechanism- This work also demonstrates the use and usefulness of a new technique (high-resolution electron energy loss spectroscopy) in this laboratory. Molybdenumdisulfide, Electron energy loss spectroscopy, Surface vibrational spectroscopy, Layer-lattice compounds.

High-yield production of mono- or few-layer transition metal dichalcogenide nanosheets by an electrochemical lithium ion intercalation-based exfoliation method

Abstract: Transition metal dichalcogenide (TMD) nanomaterials, especially the mono- or few-layer ones, have received extensive research interest owing to their versatile properties, ranging from true metals (e.g., NbS2 and VSe2) and semimetals (e.g., WTe2 and TiSe2) to semiconductors (e.g., MoS2 and We2) and insulators (e.g., HfS2). Therefore, the reliable production of these nanomaterials with atomically thin thickness and laterally uniform dimension is essential for their promising applications in transistors, photodetectors, electroluminescent devices, catalysis, energy conversion, environment remediation, biosensing, bioimaging, and so on. Recently, the electrochemical lithium ion intercalation-based exfoliation method has emerged as a mature, efficient and promising strategy for the high-yield production of mono- or few-layer TMD nanosheets; monolayer MoS2 (yield of 92%), monolayer TaS2 (yield of 93%) and bilayer TiS2 (yield of 93%) with lateral dimensions of ~1 µm (refs. 1-3). This Protocol describes the details of experimental procedures for the high-yield synthesis of mono- or few-layer TMDs and other inorganic nanosheets such as MoS2, WS2, TiS2, TaS2, ZrS2, graphene, h-BN, NbSe2, WSe2, Sb2Se3 and Bi2Te3 by using the electrochemical lithium ion intercalation-based exfoliation method, which involves the electrochemical intercalation of lithium ions into layered inorganic crystals and a mild sonication process. The whole protocol takes 26-38 h for the successful production of ultrathin inorganic nanosheets.