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 m(2) 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. (c) 2019 Elsevier Ltd. All rights reserved.