title: Liquid crystal size selection of large-size graphene oxide for size-dependent N-doping and oxygen reduction catalysis.
abstract: Graphene oxide (GO) is aqueous-dispersible oxygenated graphene, which shows colloidal discotic liquid crystallinity. Many properties of GO-based materials, including electrical conductivity and mechanical properties, are limited by the small flake size of GO. Unfortunately, typical sonochemical exfoliation of GO from graphite generally leads to a broad size and shape distribution. Here, we introduce a facile size selection of large-size GO exploiting liquid crystallinity and investigate the size-dependent N-doping and oxygen reduction catalysis. In the biphasic GO dispersion where both isotropic and liquid crystalline phases are equilibrated, large-size GO flakes (>20 μm) are spontaneously concentrated within the liquid crystalline phase. N-Doping and reduction of the size-selected GO exhibit that N-dopant type is highly dependent on GO flake size. Large-size GO demonstrates quaternary dominant N-doping and the lowest onset potential (-0.08 V) for oxygen reduction catalysis, signifying that quaternary N-dopants serve as principal catalytic sites in N-doped graphene.
authors.affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 305-701, Korea.
authors.forename: Kyung Eun
authors.initials: KE
authors.lastname: Lee
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Kim
authors.forename: Uday Narayan
authors.initials: UN
authors.lastname: Maiti
authors.forename: Joonwon
authors.initials: J
authors.lastname: Lim
authors.forename: Jin Ok
authors.initials: JO
authors.lastname: Hwang
authors.forename: Jongwon
authors.initials: J
authors.lastname: Shim
authors.forename: Jung Jae
authors.initials: JJ
authors.lastname: Oh
authors.forename: Taeyeong
authors.initials: T
authors.lastname: Yun
authors.forename: Sang Ouk
authors.initials: SO
authors.lastname: Kim
keywords: catalyst; doping; graphene; liquid crystal; oxygen reduction reaction