Hierarchically porous Co@N-doped carbon fiber assembled by MOF-derived hollow polyhedrons enables effective electronic/mass transport: An advanced 1D oxygen reduction catalyst for Zn-air battery

Developing advanced oxygen reduction reaction (ORR) electrocatalysts with rapid mass/electron transport as well as conducting relevant kinetics investigations is essential for energy technologies, but both still face ongoing challenges. Herein, a facile approach was reported for achieving the highly dispersed Co nanoparticles anchored hierarchically porous N-doped carbon fibers (Co@N-HPCFs), which were assembled by core-shell MOFs-derived hollow polyhedrons. Notably, the unique one-dimensional (1D) carbon fibers with hierarchical porosity can effectively improve the exposure of active sites and facilitate the electron transfer and mass transfer, resulting in the enhanced reaction kinetics. As a result, the ORR performance of the optimal Co@N-HPCF catalysts remarkably outperforms that of commercial Pt/C in alkaline solution, reaching a limited diffusion current density (J) of 5.85 mA cm−2 and a half-wave potential (E1/2) of 0.831 V. Particularly, the prepared Co@N-HPCF catalysts can be used as an excellent air-cathode for liquid/solid-state Zn-air batteries, exhibiting great potentiality in portable/wearable energy devices. Furthermore, the reaction kinetic during ORR process is deeply explored by finite element simulation, so as to intuitively grasp the kinetic control region, diffusion control region, and mixing control region of the ORR process, and accurately obtain the relevant kinetic parameters. This work offers an effective strategy and a reliable theoretical basis for the engineering of first-class ORR electrocatalysts with fast electronic/mass transport.