Hierarchical carbon with microporous core and mesoporous shell for efficient oxygen reduction application

We synthesize for the first time a novel carbon structure, i.e., "hierarchical core-shell carbon" (HCSC), featuring ordered microporous carbon core and mesoporous carbon shell. The preparation of HCSC is achieved through a two-step approach starting from the formation of hierarchical core-shell zeolite Y (HCSY) in a controllable etching, followed by a chemical vapor deposition using HCSY as the template. The ordered micropores in HCSC provide high specific area and abundant active sites, while the mesoporous shell enhances its efficient mass transfer, making HCSC promising potential as a catalyst support. As a demonstration, HCSC is doped with nitrogen and loaded with Fe single atom (Fe-N/HCSC) and used as an oxygen reduction reaction (ORR) electrocatalyst, exhibiting exceptional catalytic performance in 0.1 M KOH electrolyte, with an onset potential of 1.01 V and a half -wave potential of 0.915 V, significantly higher than those achieved by the commercial 20 wt% Pt/C catalyst. The superior catalytic activity of Fe-N/HCSC is attributed to the mesoporous carbon shell, improving mass transfer efficiency and enhances the accessibility of micropores, enabling the highly dispersed Fe-NX sites to fully utilize their catalytic activity. This study offers an effective solution to address the challenges associated with mass transfer in microporous materials.