Graphene and graphene-based materials are a very promising class of the robust and attractive electrode materials for the breakthrough electrochemical energy devices due to the unique layered structures and outstanding properties. Inspired by the great success of graphene, graphene-like 2D materials, including transition metal dichalcogenides, phosphorene, Mxene, covalent organic frameworks, and others, have sputtered extensive interest, particularly with mono- or multi-layered nanosheets for energy devices. However, synthesis, self-assembly and functionalization of graphene and 2D materials for fundamental understanding still remain great challenges. Therefore, the goal of our research is to design, synthesize, processing, and assembly a brand new generation of graphene and 2D materials with exquisite control of chemical composition, structural morphology and physical dimension, to fundamentally characterize and investigate their chemical and physical properties, and to develop the novel interracially integrated functional materials with different compositions, structures or properties, and eventually to create multiple nanoenergy systems with unprecedented performance to go beyond the limits of the current technologies.
To this end, we are employing top-down and bottom-up approaches to synthesize a wide range of graphene and other electrochemically active 2D nanosheets. We further explore various solution-processable assembly methods for the van der Waals integration of different nanosheets to engineer novel nanoarchitectures with new functions.
Top-down and Bottom-up Synthesis. Scalable preparation of high-quality graphene and related 2D nanosheets will basically lie in the top-down methods, e.g., chemical exfoliation, and electrochemical exfoliation of the layered materials to nanosheets, with controlled thickness, large lateral size and yield higher than 50wt%. Other methods, e.g., chemical self-assembly, template and bottom-up methods, e.g., chemical vapor phase deposition will be also performed to prepare these atomically thin, electrochemically active nanosheets.
Nanostructure Assembly. The organization and assembly of the functional moieties on electrochemically active 2D nanosheets with well-defined nanoarchitectures is highly important for fundamentally studying structure-property correlations and creating high energy electrochemical devices. Using template method, sol-gel route and other self-assembly techniques, we can integrate different nanosheet-based materials that are normally incompatible and control how the related synthetic nanosheets will generate novel complex 2D and 3D hierarchically nanostructural systems, e.g., 2D sandwich-like mesoporous nanosheets, 3D hierarchical porous networks and their hybrid nanostrcutures.
Fundamental Characterization. Surface and interface engineering and integration of atomically thin 2D materials with the combined new properties and new functions are essential to improve the electrochemical performance of nanosheet-based electrode materials for energy devices. Using a number of morphological, structural, compositional, chemical, electronic characterization techniques, we investigate the fundamentally new properties of these nanosheet-based architectures and their hybrid systems.
1.Synthesis of High-Quality Graphene with a Pre-Determined Number of Layers. Carbon, 2009, 47 (2): 493-499.
2.Synthesis of Graphene Sheets with High Electrical Conductivity and Good Thermal Stability by Hydrogen Arc Discharge Exfoliation. ACS Nano, 2009, 3 (2): 411-417.
3.Organic Radical-Assisted Electrochemical Exfoliation for the Scalable Production of High-Quality Graphene. J. Am. Chem. Soc., 2015, 137 (43): 13927-13932.
4.Field Emission of Single-Layer Graphene Films Prepared by Electrophoretic Deposition. Adv. Mater., 2009, 21 (17): 1756-1760.
5.Layer-by-Layer Assembled Heteroatom-Doped Graphene Films with Ultrahigh Volumetric Capacitance and Rate Capability for Micro-Supercapacitors. Adv. Mater., 2014, 26 (26): 4552-4558.
6.Patterning Two-Dimensional Free-Standing Surfaces with Mesoporous Conducting Polymers. Nat. Commun., 2015, 6 (6): 8817-8825.