Hierarchical CoFe@N-Doped Carbon Decorated Wood Carbon as Bifunctional Cathode in Wearable Zn-Air Battery

Rechargeable Zn-air batteries (ZAB) have drawn extensive attention due to their eco-friendliness and safety. However, the lack of high-performance and low-cost oxygen redox reactions (OER and ORR) catalysts has become one of the main stumbling blocks in their development. Herein, we successfully fabricate a CoFe nanobubble encapsulated in nitrogen-doped carbon nanocage on wood carbon support (CoFe@NC/WC) via pyrolysis of a novel Prussian blue analog (PBA)/spruce precursor. The hierarchical CoFe@NC/WC catalyst exhibits an excellent potential difference of 0.74 V between the OER potential at 10 mA cm^-2 and half-wave potential of ORR in 0.1 M KOH, comparable to recently reported preeminent electrocatalysts. Further, CoFe@NC/WC shows outstanding electrochemical performance in liquid ZAB, with a peak power density of 138.9 mW cm^-2 and a specific capacity of 763.5 mAh g^-1. More importantly, a bacterial cellulose nanofiber reinforced polyacrylic acid (BC-PAA) hydrogel electrolyte shows ultrahigh tensile-breaking stress of 1.58 MPa. In conjunction with the as-prepared CoFe@NC/WC catalyst, BC-PAA-based wearable ZAB displays impressive rechargeability and foldability, and can power portable electronics, such as electronic timer and mobile phone, in bent states. This work provides a new approach toward high-activity and low-cost catalysts for ZAB.