Cobalt nanoparticles-encapsulated holey nitrogen-doped carbon nanotubes for stable and efficient oxygen reduction and evolution reactions in rechargeable Zn-air batteries

A new, simple, and inexpensive approach for fabricating electrocatalysts is developed to optimize oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) efficiency rechargeable Zn-air batteries. Holey N-doped carbon nanotubes (H-NCNT) are prepared by a simple reaction, and then Co nanoparticles are encapsulated inside the H-NCNT (Co@H-NCNT) through the holes of the H-NCNT. Electrocatalytic activities of Co@H-NCNT toward ORR and OER are explored, and comparable to those of the Pt/C and IrO2. This is because the core-shell microstructure of Co@H-NCNT effectively forms catalytic active sites. Density functional theory (DFT) calculation reveals that the active sites in Co@H-NCNT have low overpotentials for ORR and OER, resulting in excellent catalytic activities. A Zn-air battery using Co@H-NCNT exhibits excellent power density (207.0 mW/cm2) and stability after 300 cycles. Therefore, Co@H-NCNT is a promising bi-functional ORR and OER catalyst for efficient electrocatalysis in Zn-air batteries with superior energy capacity and cycle durability.