Doped Graphene Nanoribbons: Synthesis, Characterization and Application

Abstract

Graphene nanoribbons (GNRs), narrow elongated strips of graphene with ultra-high aspect ratios and abundant edges, have recently become a harbinger of novel carbon nanomaterials due to their versatile properties, particularly if synthesized by unzipping of multiwalled carbon nanotubes (MWCNTs). GNRs have been investigated for the fabrication of polymer nanocomposites, and for use in batteries, supercapacitors and fuel cells owing to the high available surface area and active edge sites, high mechanical strength and electrical conductivity, and the scalability of the synthesis. They could also find applications for peptide mediated drug delivery in biomedicine, and as intrinsically fluorescent nanoparticles in nanotoxicology studies. In this dissertation, MWCNTs with different geometrical characteristics and chemical functionalities have been synthesized, and attempted to unzip via chemical and electrochemical oxidation methods. Upon successful unzipping, some of the carbon atoms in the sp2 network of the product graphene oxide nanoribbons (GONRs) have been substituted by a variety of heteroatoms of approximately the same radius, such as nitrogen, boron and sulfur. Microstructural features, structural defects, crystallinity, thermal stability, and elements and their functional groups have been studied using a wide range of characterization techniques. Finally, doped GNRs nanomaterials have been used as carbon-based electrocatalysts for oxygen reduction reaction (ORR) in alkaline and acidic electrolytes. The results have shown that bamboo structured MWCNTs have been unzipped through helical and dendritic mechanisms, which are substantially different from the longitudinal unzipping of open channel MWCNTs. The resultant GNRs nanomaterials with a multifaceted structure and active edge sites have competed with the current state-of-the-art platinum-based electrocatalysts in all of the key ORR properties: onset potential, exchange current density, four electron pathway selectivity, kinetic current density, stability and methanol tolerance. Such GNRs would have potential applications in the cathodes of metal-air batteries, and alkaline and proton-exchange membrane fuel-cells.