Highly Exposed Active Sites of Defect-Enriched Derived MOFs for Enhanced Oxygen Reduction Reaction

The low utilization of active sites of metal–organic framework (MOF)-derived nanostructured carbon materials are considerable challenges in practical applications. Here, we develop MOF (ZIF-8)-derived N-doped porous carbon (NPC) nanomaterials as high active oxygen reduction reaction (ORR) catalysts which are enhancing both the exposed active sites and surface defects of NPC resulting from the enlarged pore of NPC by KOH activation strategy. The experiments show that the KOH activation not only enlarged the pore size of ZIF-8-derived NPC nanomaterials creating numerous mesopores but also generated abundant defects in NPC nanomaterials. The 4 h KOH-activated MOF-derived NPC (NPC-4) nanomaterials show an activity of 0.257 mA cm–2 at 0.9 V (vs reversible hydrogen electrode), which was almost 10 times greater than that of NPC nanomaterials (0.0265 mA cm–2). The NPC-4 exhibits a comparable ORR activity, higher stability, and better tolerance to methanol compared with the commercial Pt/C. The density functional theory results show that N-doped carbon along with the defects is more favorable for ORR compared with N-doped carbon because the presence of defects leads to enhanced O adsorption ability and promotes the ORR process.