Hierarchically porous doped carbons fabricated by the strategy of ion transfer coordination (ITC)

The hierarchical pore structures of carbon are important for diffusion-limited applications. The macro/mesopores of carbon are often produced by using a template while the micropores originate from pyrolysis shrinkage or activation. Herein, the templates of the zeolitic imidazolate frameworks (ZIFs) are etched into Zn²⁺ and ligands during the formation of the polydopamine (PDA) shell, and then the zinc ions are transferred into the PDA shell, constructing the Zn²⁺-coordinated PDA nanobubbles. These nanobubbles are pyrolyzed into the N-doped carbon nanobubbles. During carbonization, the PDA-coordinated Zn ions are reduced into metallic zinc, and then it is vaporized above its boiling-point temperature, thus creating numerous micropores in the resulting carbons. Meanwhile, the etching of ZIF templates generates abundant macro/mesopores. This ion transfer coordination (ITC) strategy facilitates the in situ formation of the micropore template of metallic zinc. As an extension of this ITC strategy, the Zn²⁺/Fe³⁺-coordinated PDA nanobubbles are prepared and then pyrolyzed into Fe single-atom doped carbons with hierarchical pore structures. These hierarchically porous carbons exhibit superior catalytic performances for the oxygen reduction reaction. This ITC strategy opens up a novel pathway to fabricate metal-free and single-atom doped carbons with hierarchical pore-structures for diffusion-limited applications.