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 frameworks (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 incorporation 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 (Eonset) and the half-wave potential (E1/2) on Co–N/PCNs-2 are 0.99 V and 0.88 V, respectively, outperforming the commercial Pt/C (Eonset = 0.98 V, E1/2 = 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-NX active site along with the defects are conducive to the O2 adsorption and thus improve the ORR process compared with the pure Co-NX active site.