Ag Decorated Co 3 O 4 -Nitrogen Doped Porous Carbon as the Bifunctional Cathodic Catalysts for Rechargeable Zinc-Air Batteries

The use of transition metals as bifunctional catalysts for rechargeable zinc-air batteries has recently attracted much attention. Due to their multiple chemical valence states, the cobalt oxides are considered to be promising catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this work, bifunctional Ag-decorated Co 3 O 4 -nitrogen doped porous carbon composite (Co 3 O 4 -NC&Ag) catalysts were synthesized by annealing ZIF-67 in N 2 and O 2 , respectively, followed by Ag deposition using chemical bath deposition. Due to the decoration of Ag nanoparticles and high specific surface area (46.9 m 2 g −1 ), the electrochemical activity of Co 3 O 4 increased significantly. The optimized Co 3 O 4 -NC&Ag catalysts possessed superior ORR performance with a half-wave potential of 0.84 V (vs. RHE) and OER activity with an overpotential of 349 mV at 10 mA cm −2 . The open circuit voltage of the Co 3 O 4 -NC&Ag-based zinc-air battery was 1.423 V. Meanwhile, the power density reached 198 mW cm −2 with a specific discharge capacity of 770 mAh g −1 at 10 mA cm −2 , which was higher than that of Pt/C-based zinc-air battery (160 mW cm −2 and 705 mAh g −1 ). At a current density of 10 mA cm −2 , the charge-discharge performance was stable for 120 h (360 cycles), exhibiting better long-term stability than the Pt/C&RuO 2 counterpart.