Tailored carbon nanostructures via graphitic surface modification and their applications

Abstract

Atomic level engineering of graphitic surface of graphene-based materials is highly demanded for the customized structures and properties aiming at different applications. Unzipping of graphene plane is a strong candidate to this purpose, but uncontrollable damage of the two-dimensional crystalline framework during harsh unzipping reaction has remained as the key challenge. In this thesis, we present heteroatom dopant-specific unzipping of carbon nanotubes as a reliable and controllable route to customized intact crystalline graphene-based nanostructures. Substitutional pyridinic nitrogen dopant sites at carbon nanotubes can selectively initiate the unzipping of graphene side walls at a relatively low electrochemical potential (0.6 V). The resultant nanostructures consisting of unzipped graphene nanoribbons wrapping around carbon nanotube cores maintain the intact two-dimensional crystallinity with well-defined atomic configuration at the unzipped edges. Large surface area and robust electrical connectivity of the synergistic nanostructure demonstrates ultrahigh-power supercapacitor performance, which can serve for AC filtering with the record-high rate-capability of -85º of phase angle at 120 Hz. The controllable manner of dopant-specific unzipping allows to manipulate doping concentration for property tuning of graphitic carbons. The produced oxygen-functionalized edges, which are potential site for target dopants, facilitate the incorporation of the desired amount of dopant. Suitable surface energy (wettability), tuned electronic structure (the Fermi energy level) and enhanced electrostatic interaction (protonation of pyrinidic nitrogen) are achieved by controlled unzipping and subsequent nitrogen doping. Taking advantage of the property tuning, we demonstrate efficient synthesis of metal- or metal oxide-graphitic carbon hybrids, such as Au nanoparticle-NCNT, Pt nanoparticle-NCNT and MnOx-NCNT hybrids, and improve the performance of diverse electrochemical applications, such as oxygen reduction reaction catalyst, bio-sensors and pseudo-capacitors.