Font Size: a A A

Graphene Nanoribbon-based Nanocomposites: Preparation, Performance And Applications

Posted on:2015-07-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:M K LiuFull Text:PDF
GTID:1221330464461480Subject:Polymer Chemistry and Physics
Abstract/Summary:PDF Full Text Request
Graphene nanoribbon (GNR) is a quasi one-dimensional carbon material which is composed of tightly packed monolayer of carbon atoms. GNRs were originally studied by Fujita and co-workers as a theoretical model to examine the edges and nanoscale size effect of graphene sheets. After GNRs with controlled edge orientation have been fabricated by scanning tunneling microscope lithography by Levente and co-workers, GNRs had attracted a great number of attentions from researchers. GNRs not only own good physical and chemical properties of graphene sheets, but also have unique edge states, resulting in their characteristic properties. Experimental results apparently show that the energy gaps of GNRs can be increased with the decrease of their width, and the electronic states can be changed from semi-conductor to metallic conductor. Moreover, GNRs have large aspect ratio and high plane integrity. These features endow GNRs with tremendous research interest. However, pure GNRs have drawbacks such as aggregation tendency, as well as poor performance when simply used as electrode materials in energy conversion and storage systems, which hinder their further applications in the fields of materials science. Hybridizing GNRs with other functional nanomaterials to form GNRs-based nanocomposites with hierarchical structures is an effective way to solve the application problems of pure GNRs. Up to now, fabrication of GNRs-based nanocomposites by combining GNRs with functional nanomaterials and realizing their synergistic effect has become a hot research point in scientific community. Meanwhile, developing new methods to simplify the preparation process of GNRs or their nanocomposites is an urgent task with great interest.Based on the problems and tasks discussed above, we have prepared hybrid nanomaterials (GNR/CNT) of GNRs and carbon nanotubes (CNTs) by partially unzipping the pristine multi-walled CNTs, and further explored their application in energy conversion system. We also have prepared nanocomposites by hybridizing GNR/CNT with organic or inorganic nanomaterials such as polyaniline (PANI) and Ni(OH)2, as well as GNR/MnO2 hybrid nanomateials, and further study their performance as electrode materials in supercapacitors. The main research achievements in this dissertation are listed as follows:(1) Hybrid nanomaterials of GNR/CNT have been prepared via a one-step method of longitudinal unzipping of multi-walled CNTs, and were further used as counter electrode materials in the energy conversion device of dye-sensitized solar cell. By adjusting the amount of oxidant (KMn.04) used in the unzipping process, multi-walled CNTs have been unzipped at different extents. By acting as "bridges", the GNRs connected different CNTs to form a three-dimensional conductive network, which facilitates the rapid transfer of charges or electrons. And the excellent catalytic activity of the active sites in the edges of GNRs can be fully utilized. Furthermore, the existence of residual CNTs helps the formation of porous structure inside GNR/CNT hybrid. These features effectively enhance the performance of GNR and largely expand the application fields of GNR-based nanomaterials.(2) Nanocomposite (GNR/CNT/PANI) of GNR/CNT and PANI has been prepared by in-situ polymerization of aniline monomers on the surface of GNR/CNT hybrid. The in-situ polymerization process ensures close contact between PANI and GNR/CNT hybrid, and the GNR/CNT hybrid can also play a role of "skeleton" inside PANI materials to facilitate the rapid transfer of charges. Also, the porous structure of GNR/CNT/PANI nanocomposite assures fast transmission of electrolyte ions and contributes to the good performance of device. This effective hybridization of GNR/CNT and PANI can realize the synergistic effect of electrode double layer capacitance of GNR/CNT and pseudocapacitance of PANI. The all-solid-state supercapacitor based on this GNR/CNT/PANI material exhibits superior performance such as high specific capacitance, low resistance as well as good cycle life, which further expand the application of GNR-based nanomaterials.(3) Nanocomposite (GNR/CNT/Ni(OH)2) of GNR/CNT and Ni(OH)2 has been prepared by synthesizing Ni(OH)2 nanoparticles on the surface of GNR/CNT hybrid via a hydrothermal method. The GNR/CNT hybrid acts as a basal body by providing excellent electrical conductivity to ensure the loading of Ni(OH)2 nanoparticles. The GNR/CNT hybrid also has good chemical stability which helps the thorough exploitation of the pseudocapacitance of Ni(OH)2 nanoparticles and enhances its long term stability. Acting as electrode material in supercapacitor, GNR/CNT/Ni(OH)2 nanocomposite shows higher specific capacitance, which is higher than the performance of the individual component, indicating that the synergistic effect has been achieved between GNR/CNT and inorganic nanomaterials within the nanocomposite.(4) Three-dimensional hierarchical hybrid nanomaterials (GNR-MnO2) of graphene nanoribbons (GNRs) and MnO2 nanoparticles have been prepared via a one-step method. In this work, not only the CNTs have been totally unzipped but also the uniform deposition of MnO2 nanoparticles on the surface of GNRs has been realized. With the GNR-MnO2 hybrid as the positive electrode and GNR sheets as the negative electrode, asymmetric supercapacitor has been fabricated and exhibits excellent electrochemical properties such as enlarged working potential (2.0 V) and great enhanced energy density (29.4 Wh kg-1). This greatly enhanced energy storage ability and high rate capability can be attributed to homogeneous dispersion and excellent pseudocapacitive performance of MnO2 nanoparticles and high electrical conductivity of the GNRs.
Keywords/Search Tags:carbon nanotubes, graphene nanribbons, hybrid materials, supercapacitor, dye-sensitized solar cell
PDF Full Text Request
Related items