Synthesis of carbon nanosheets with numerous nanopores

   An international research team led by NIMS and Waseda University has succeeded in synthesizing carbon nanosheets with numerous pores. When poreless two-dimensional nanosheets are stacked, their specific surface areas decrease significantly, reducing their electrochemical performance. This team developed a technique for synthesizing porous carbon nanosheets by exfoliating layered metal–organic frameworks (MOFs) into individual nanosheets and carbonizing them. These nanosheets can be re-stacked to form three-dimensional materials while preserving many of their catalytically active sites.

   Basically MOFs consist of organic building units and metal ions linked by organic ligands. They can be used to effectively adsorb, separate or recognize gaseous molecules. However, their less conductivity makes them ineffective for a wide range of electrochemical applications, including electrocatalysts, capacitors, rechargeable batteries, and fuel cells. MOF-derived porous carbons with chemically stable and electrically conductive frameworks are expected to exhibit high performance for these applications.

   This team recently developed porous carbon nanosheets only 1.5 nm in thickness with numerous, completely penetrating pores across them. New functions can be easily imparted to them by chemically modifying their pores using other molecules. For example, MOFs can be exfoliated and carbonized to form porous carbon nanosheets while preserving MOF-derived nitrogen atoms (N). The pores of the nanosheets can then be modified with iron atoms (Fe) to form uniformly and densely distributed electrochemically active Fe-N₄ sites across the nanosheets. These nanosheets can potentially be used to significantly increase oxygen reduction reaction (ORR) activities under acidic conditions in fuel cells. The porous carbon nanosheets developed by this team will potentially exhibit high performance in a wide range of electrochemical processes, including energy conversion and storage.

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   This project was carried out by an international research team led by Yusuke Yamauchi (Leader of the Mesoscale Materials Chemistry Group, International Center for Materials Nanoarchitectonics (MANA), NIMS; Professor, University of Queensland, Australia; Visiting Professor, Waseda University; Director of the Yamauchi Materials Space-Tectonics Project funded by JST’s ERATO program) and researchers from Waseda University, the University of Queensland, East China Normal University and the Nanjing University of Aeronautics and Astronautics. This work was conducted as part of the Yamauchi Materials Space-Tectonics Project.

   This research was published in the online version of the Journal of the American Chemical Society on May 23, 2022, Japan Time.