ZIF-8@ZIF-67-derived ZnCo2O4@nitrogen-doped carbon/carbon nanotubes wrapped by a carbon-layer: a stable oxygen reduction catalyst with a competitive strength in acid media

Abstract Due to the sluggish reaction kinetics and poor stability of cathodic catalysts for oxygen reduction reaction (ORR) in acidic media, the development of highly-active and acid-stable ORR catalysts is of great practical significance. Herein, the prepared ZIF-8@ZIF-67 material, polyvinylpyrrolidone (PVP), and expanded graphite (EG) are used as precursors to prepare the ZnCo2O4@nitrogen-doped carbon-carbon nanotubes wrapped by a PVP-derived thin carbon-layer anchored on the EG (ZnCo2O4@NC-CNTs@PCL/EG) as ORR catalysts. ZnCo2O4@NC-CNTs@PCL/EG-10 (weight ratio of ZIF-8@ZIF-67 to EG is 10) has an onset potential 0.689 V (vs. SCE), which is comparable to that of commercial Pt/C (0.706 V) in acid electrolyte. After acid-pickling, the spinel ZnCo2O4 as the core is stably and uniformly encapsulated by the NC-CNTs skeleton and can fully utilize the highly-active Co2+ sites to boost the 4e– ORR process with a strong methanol resistance. ZnCo2O4@NC-CNTs@PCL/EG-10 shows the strong stability and methanol tolerance (decline of 3.21 %) after 3600 s, which are better than those of commercial Pt/C (29 mV and 4.06 %). The ORR durability is attributed to the PCL shell that avoids the corrosion of active ZnCo2O4 and N-species. Therefore, it provides a new idea for designing a spinel-based ZIFs-derivates as stable ORR catalysts in acid media.