Nanotechnologies / Materials
Smart device, Energy storage

Synthesis of high-crystallinity randomly stacked graphene
macrostructures
Department of Applied Physics, Graduate School of Engineering
PhD course student Zizhao Xu
Assistant Professor Taiki Inouehttps://researchmap.jp/inoue_t

Professor Yoshihiro Kobayashi

https://researchmap.jp/koba_ap_eng_ou

Abstract

Nanotechnologies / Materials

In this study, we developed a method to synthesize highly
crystalline and randomly stacked graphene macrostructures. By
ultra-high temperature treatment at 1500–1800 C using ethanol asa reactive gas, graphene macrostructures with high crystallinity
and high random stacking fractions were successfully synthesizedfrom sponge-shaped graphene oxide (GO) assemblies formed bya freeze-drying method. Additionally, the random stacking fractions
were further improved by adding cellulose nanofibers (CNF).

tures of GO as a starting material, sponge-like structures formedby freeze-drying resulted in higher crystallinity and higher random
stacking fractions not only on the surface but also inside the macrostructures after the ultra-high temperature treatment. We consider
that the ethanol-derived effects of carbon atom supply and defectetching can reach the interior of the GO sponges, resulting in efficient structural repair while preventing rearrangement of orientations between graphene layers.

▍ Background & Results
Graphene is a nanocarbon material with a variety of excellent
properties, but its thinness and small size limit its application fields.
Although graphene macrostructures are needed for macro-scale
applications, a simple approach results in a structure similar tographite and lost of the excellent properties of graphene. Assemblies with a high random stacking fractions prevent the degradation of properties caused by strong graphene interlayer interactions
and enable the use of the excellent properties on the macroscale.
The graphene sponge structures obtained in this study are expected to be applied in various devices including wearable strain sensors and battery electrodes.

Schematics of synthesis process of the graphene macrostructures.

▍ Significance of the research and Future perspective
Graphene is a nanocarbon material consisting of six-memberedrings of carbon atoms with a thickness of one atom. Due to its
unique electronic structure, graphene has excellent properties
and is expected to find a variety of applications. However, sincegraphene is extremely thin and small, it is necessary to synthesize
graphene macrostructures for macro-scale applications. For multilayer graphene, thermodynamically stable AB stacking structure
is preferentially formed. Then, electronic structure of multilayer
graphene is altered from that of single-layer graphene and approaches graphite due to strong interlayer interactions. On theother hand, the interlayer interaction is weak in a randomly stackedstructure. To preserve the properties of graphene and enable its
application on a macro scale, graphene macrostructures with highcrystallinity and high random stacking fractions need to be synthesized.
In this study, we synthesized graphene macrostructure samples
by various processes from graphene oxide (GO) and evaluatedtheir crystallinity and random stacking fractions by Raman spectroscopy and other techniques. We found that the crystallinity andrandom stacking fractions of graphene microstructures were improved significantly when treated at ultra-high temperatures withethanol as a reactive gas compared to when treated with inert
argon. Furthermore, compared to the dense aggregated struc-(a) Raman spectra and (b,c) scanning electron microscope images of thegraphene macrostructures.

P a t e n t
Xu, Zizhao; Inoue, Taiki; Nishina, Yuta et al. Stacking Order Reduction in Multilayer Graphene by Inserting Nanospacers. Journal of Applied Physics. 2022,132, p. 174305, doi: 10.1063/5.0103826
Xu, Zizhao; Nakamura, Shingo; Inoue, Taiki et al. Bulk-scale synthesis of randomly stacked graphene with high crystallinity, Carbon. 2021, 185, p. 368375, doi: 10.1016/j.carbon.2021.09.034
UR
L http://www.ap.eng.osaka-u.ac.jp/nanomaterial/index.html
K e y w o r d nanocarbon materials, reduced graphene oxide, interlayer interaction
Tr e a t i s e