An innovative synthetic approach for core-shell multiscale hierarchically porous boron and nitrogen codoped carbon nanofibers for the oxygen reduction reaction

In this work, polyacrylonitrile (PAN) and metal-organic framework (MOF)-derived 3D B and N codoped core-shell carbon nanofibers (CNFs) with multiscale carbon layers derived from continuous zeolitic imidazolate frameworks (ZIF-8 and ZIF-67) are synthesized via dual-functional ZnO and Co3O4 nanostructures. Here, ZnO and Co3O4 act as a metal-ion source for the MOF formation and as pore creating agents. Further, dual-function NaBH4 reduces metallic ions into respective metals as well as providing three-dimensionality to the conventional two dimensional CNF mat. Additionally, B and N doping can be achieved by treatment with a single dopant, NH4HB4O7·3H2O. The resulting core-shell multiscale-3D CNFs with hierarchical pores (ZIF-8@BN-CNF) deliver exceptional onset (0.94 V vs RHE) and half wave potential (0.86 V vs RHE)) with excellent cyclic stability toward the oxygen reduction reaction (ORR). Moreover, the electrode maintained a remarkably high current retention of 97.2%, even after 25 000 s, which is better than that of a commercial Pt/C catalyst (89.6%). The superior catalytic activity and stability of the CNF-based catalyst are attributed to the synergistic effect of the structure and codoping of B and N with highly porous 3D hierarchical core-shell nanoarchitecture. [Display omitted] •3D-porous B and N codoped core-shell CNFs are fabricated from PAN/MOFs moiety.•Hierarchical-3D CNFs electrodes are employed as metal-free electrocatalyst for ORR.•ZIF-8@BN-CNF electrode delivers highly positive half wave potential (0.86 V vs RHE).•The catalyst also delivers excellent stability and methanol tolerance activity.