Ultrathin Co(OH)2 Nanosheets@Nitrogen-Doped Carbon Nanoflake Arrays as Efficient Air Cathodes for Rechargeable Zn-Air Batteries.

Developing highly active, cost-effective, and durable bifunctional oxygen electrocatalysts is an important step for the advancement of rechargeable Zn-air batteries (ZABs). Herein, an efficient bifunctional oxygen electrocatalyst of ultrathin Co(OH)2 nanosheets supported on nitrogen-doped carbon nanoflake arrays (named as Co(OH)2 @NC), is reported, which yields excellent bifunctional activity, i.e., a low overpotential of 285 mV to reach 10 mA cm-2 for oxygen evolution reaction (OER), a high half-wave potential (0.83 V) for oxygen reduction reaction (ORR), and a low potential gap (ΔE) of 0.69 V. The excellent bifunctional catalytic performance can be ascribed to the concerted efforts of cobalt hydroxide toward OER and nitrogen-doped carbon for ORR. The Co(OH)2 @NC nanoflake arrays is further used as binder-free air cathodes for rechargeable Zn-air batteries, exhibiting a high specific capacity of 798.3 mAh gZn -1 , improved stability (a working life of >70 h at 5 mA cm-2 ), as well as a reduced long-term charging voltage, which outperforms the counterparts of NC nanoflake arrays and Pt/C-based air cathodes. One step further, the Co(OH)2 @NC nanoflake arrays on carbon cloth are directly used as binder-free air cathodes for flexible, solid-state ZABs, showing excellent performance under deformation as well.