Nanoarchitecturing Carbon Nanodot Arrays on Zeolitic Imidazolate Framework<i>-</i>Derived Cobalt<i>–</i>Nitrogen<i>-</i>Doped Carbon Nanoflakes toward Oxygen Reduction Electrocatalysts
Yongqi Yin, Jie Wang, Tao Li, Jonathan P. Hill, Alan E. Rowan, Yoshiyuki Sugahara, Yusuke Yamauchi
Abstract
Two-dimensional (2D) nanoporous heterostructured composites formed by uniformly coating individual monolayers with porous layers introduce unparalleled opportunities to improve and optimize the electrochemical performances of 2D materials. Here, an all-porous carbon heterostructure composed of 2D microporous carbon nanoflakes uniformly decorated with carbon nanodots has been developed. Interestingly, resol-F127 micelles self-assemble on the surface of zeolitic imidazolate framework (ZIF) nanoflakes in the form of a nanodot array, yielding a heterostructure. Hydrothermal treatment followed by carbonization under a nitrogen atmosphere causes conversion of the nanodot–nanoflake assembly into a carbon-based material composed of hollow carbon nanodots (CNDs) and microporous carbon nanoflakes (CNFs), that is, a CND@CNF composite. The combination of 2D microporous carbon nanoflakes with carbon hollow nanodots enhances exposure of the active sites and improves mass transfer in all directions (including through the nanoflakes). The use of cobalt (Co)-containing ZIF leads to the synthesis of a Co–Nx-doped CND@CNF composite, which exhibits oxygen reduction reaction electrocatalytic activity and long-term stability superior even to commercial Pt/C catalysts. This architecture-engineering strategy has been used to design and synthesize 2D heterostructures possessing high electrocatalytic efficiency and will be useful for future developments in important electrochemical energy storage and conversion applications.