Hierarchical architecture derived from two-dimensional zeolitic imidazolate frameworks as an efficient metal-based bifunctional oxygen electrocatalyst for rechargeable Zn–air batteries

Design and synthesis of efficient and inexpensive bifunctional electrocatalysts for oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) is crucial and urgent for the applications of Zn-air batteries. Inspired by rapid development of metal organic framework (MOF)-derived materials in various applications, a novel MOF-derived 1D-on-2D hierarchical structure is developed by a facile wet chemical method and pyrolysis process. Specifically, the hierarchical structure (Co-NCS@CNT) consists of 2D carbon framework covered with copious N-doped carbon nanotubes (CNTs) with highly-dispersed cobalt nanoparticles encapsulated within their tips. Abundant Co-N-C active sites, large specific surface area (396 m2 g−1), rapid mass/electron transport and high electrical conductivity enable Co-NCS@CNT with a high ORR half-wave potential of 0.86 V and low OER overpotential of 360 mV at 10 mA cm−2. Moreover, compared with commercial Pt/C-Ir/C catalysts, primary and rechargeable Zn-air batteries based on Co-NCS@CNT exhibit a higher peak power density (90 mW cm−2), specific capacity (798 mAh g−1), open circuit potential (1.42 V) and better stability. Therefore, this work provides a facile, low cost and environmental-friendly strategy to rational design and synthesize micro-structures for bifunctional catalyst materials for zinc-air batteries and other devices.