Constructing macroporous nanofibers with enriched Co–N–C sites via a cascade chamber confinement strategy for an efficient oxygen reduction reaction

Due to the thermal migration and aggregation of metal atoms, constructing nonprecious-metal and N-doped carbon (M-N-C) materials with unique pore structures, highly accessible surface area, and dense metal active sites by pyrolysis remains a challenge. Here we report a cascade chamber confinement approach to fabricate Co-N-C nanofibers with continuous macro-porous carbon nanofiber networks and dense Co-N-C sites. The central objective of this method is to confine Co²⁺ through cascade chambers of zeolitic imidazolate frameworks (ZIFs) and cross-linked nanofiber networks, thus preventing Co agglomeration at high temperatures and resulting in a free-standing film with high dispersion of Co active sites via facile electrospinning. The interconnected hierarchical pores of the nanofiber film offer highly exposed accessible active sites and fast mass transfer. Resultantly, it exhibits encouraging oxygen reduction reaction catalytic activity with a half-wave potential of 0.82 V (vs. RHE), which is higher than that of Co-N-C electrocatalysts prepared without limited protection. This strategy is widely applicable to different metal-containing precursors and opens up new possibilities to fabricate M-N-C materials with high-density metal sites as electrocatalysts for an efficient oxygen reduction reaction.