Defect-enriched hollow porous Co-N-doped carbon for oxygen reduction reaction and Zn-Air batteries

The precise control of morphology and structure of porous carbon derived from metal-organic frame-works (MOFs) is crucial for determining the oxygen reduction reaction (ORR) activity. Herein, defect-enriched hollow porous Co-N-doped carbon nanomaterials (Co-N/PCNs) towards ORR were obtained by pyrolyzing a ZIF-8 encapsulated Co ions nanocomposite. We found that the amount of the incorpo-ration of cobalt (II) into ZIF-8 precursors play very important role in the structural evolution of ZIF-8 derivatives during the high temperature pyrolysis. The experiments show that defect-enriched hollow porous Co-N-doped carbon derived from the incorporation of 2 wt% cobalt (II) into ZIF-8 precursors (Co-N/PCNs-2) showed excellent stability and activity towards ORR. The onset potential (E-onset) and the half-wave potential (E-1/2) on Co-N/PCNs-2 are 0.99 V and 0.88 V, respectively, outperforming the commercial Pt/C (E-onset = 0.98 V, E-1/2 = 0.85 V). Moreover, the Zn-air batteries with Co-N/PCNs-2 as an air electrode displays robust stability and high activity, affording a maximum power density of 135 mW cm(-2) in comparison with the Pt/C catalysts (114 mW cm(2)). The density functional theory (DFT) verified that the Co-N-X active site along with the defects are conducive to the O-2 adsorption and thus improve the ORR process compared with the pure Co-N-X active site. (C) 2020 Elsevier Ltd. All rights reserved.