String of pyrolyzed ZIF-67 particles on carbon fibers for high-performance electrocatalysis

ZIF-67 comprises alternately arranged cobalt atoms and nitrogen-rich organic linkers, making it an ideal single source precursor to producing Co and N co-doped carbon (C-ZIF-67) catalyst for oxygen reduction reaction (ORR). C-ZIF-67 particle catalyst in air-cathode, however, often shows limited activity and stability because of the particle-to-particle resistances and particle detachment issues. Herein, we introduce an in-situ approach to selectively growing ZIF-67 on electrospun polyacrylonitrile (PAN) fibers, forming an interesting “gems-on-string” structured PAN@ZIF-67 hybrid. Upon pyrolysis the hybrid is converted to conductive C-PAN@ZIF-67 with well-retained hierarchical structure, showing high ORR activity with excellent durability in alkaline electrolyte. A zinc-air battery (ZnAB) using C-PAN@ZIF-67 in air-cathode delivers a stable discharge voltage of 1.24 V at a high current density of 20 mA cm⁻². With the regeneration of the cell after its full-discharges by mechanically replenishing the zinc anode and the electrolyte, a continuous operation over 38 days is demonstrated with the discharge voltage above 1.0 V at a current density of 10 mA cm⁻². Significantly, a freestanding C-PAN@ZIF-67 mat serves directly as the flexible cathode for thin and bendable ZnABs to deliver high discharge voltages in both flat and bent states, promising great potential for future wearable electronics.