Synthesis of graphene nanoribbons and their hybridization via nitrogen-doping

Abstract

Carbon nanomaterials (e.g. carbon nanotubes, graphene) have attracted particular attentions with fascinating characteristics, such as superior charge carrier mobility, outstanding thermal conductivity, large specific surface area, and extraordinary mechanical strength. Despite of these interesting nature, there have been some limitations to satisfy many demands for further practical applications due to their intrinsic inert surface arising from their sp2 hybridized graphitic nanostructure. Therefore, covalent modification has been essential for optimizing the desired properties. To date, various covalent modification methods have been reported such as oxidative functionalization, direct covalent modification, and doping. Among them, doping has been recognized as an efficient route to control the properties. Especially, nitrogen (N) doping in graphitic lattice modifies surface energy, electronic structures giving surface reactivity and catalytic activity. However, substitutional N-doping in graphitic carbon is energetically unfavorable owing to chemically inert graphene plane. Therefore, optimized carbon nanostructure has been required to maximize the doping efficiency by lowering dopant formation energy. Graphene nanoribbon (GNR), a thin strip of graphene, has high edge to plane ratio which could be the optimal carbon framework for doping. Especially, the degree of crystallinity could significantly affect the functionality of GNR originating from its extraordinary quasi one-dimensional nanostructures. We take advantage of different crystalline GNR structures via N-doping process demonstrating remarkable performance of various GNR applications. We synthesize the GNR by unzipping of N-doped carbon nanotubes (CNTs). Synergistic two-step unzipping could make crystalline and semiconducting GNRs with a high yield. In addition, we make Ti3C2Tx MXene-GNR hybrids via N-doping inducing the strong chemical interaction demonstrating that improved interfacial adhesion could effectively reduce hysteresis for practical pressure sensor. Finally, we employed NGNR as a carbon support for platinum (Pt) single atom catalyst (SAC) revealing superior mass activity and durability for hydrogen evolution reaction (HER) in proton exchange membrane electrolysis cell (PEMEC).