Monodispersed Co in Mesoporous Polyhedrons: Fine-tuning of ZIF-8 Structure with Enhanced Oxygen Reduction Activity

•The mesoporous structures are well prepared by using Zn in Bi-MOF.•Better catalysis for ORR than commercial Pt/C catalysts in alkaline.•Efficient and Facile synthetic Method.•Atomically dispersed Co nano-particles doped mesoporous carbon.•A better strategy to avoid agglomeration of metal while heating at high temperature.

Metal organic frameworks (MOFs) have been considered as promising candidates for excellent electrocatalysts. Herein, we report a controllable synthesis of Co-N-C electrocatalysts derived from Zn/Co bimetallic organic frameworks (Zn/Co-MOFs). The elimination of Zn is simultaneously taken place during the pyrolysis due to its low boiling point, resulting in a very mesoporous assembly with homogeneous Co distribution in N-C framework. Zn also facilitates the dispersion of Co in the Zn/Co-MOF, which efficiently hinders the agglomeration of Co during carbonization. The results show that Co-N-C catalysts synthesized from 22.5% Co containing in the Zn/Co-MOF precursor gives the best ORR activity in alkaline solution with its half wave potential of 0.91 V vs. RHE and current density of 3.0 mA/cm2, which is even better than those of commercial Pt/C catalysts. The high activity and current density are mainly attributed to the extremely well dispersed Co nanoparticles and the mesoporous nature.

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