High-performance rechargeable zinc-air batteries enabled by cobalt iron anchored on nitrogen-doped carbon matrix as bifunctional electrocatalyst.

Developing efficient bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) electrocatalysts is potential ways for achieving high rechargeable zinc-air (Zn-air) battery performance. Herein, we report an iron (II) acetate-assisted strategy to synthesize CoFe-NC-OAc catalyst with cobalt iron (CoFe) alloy anchored on nitrogen-doped carbon (NC) matrix, which can serve as efficient ORR/OER bifunctional electrocatalysts for rechargeable Zn-air batteries. Apart from alloying with Co to form ORR/OER active CoFe nanoparticles, the incorporation of iron (II) acetate has expanded the pore size inside the CoFe-NC-OAc catalyst to serve as gas transfer channels, and has induced synergetic electronic coupling between CoFe nanoparticles and NC matrix for boosting catalytic activity. Therefore, CoFe-NC-OAc exhibits favorable ORR activity with a most positive half-wave potential of 0.90 V vs. RHE, fast ORR kinetics with a highest kinetic current density of 57.4 mA cm at 0.85 V vs. RHE, and fast O diffusion and transport that enables smaller mass transport overpotential at high current density up to 800 mA cm. Additionally, CoFe-NC-OAc can catalyze OER with low overpotential of 310 mV at 10 mA cm. When employed as air electrode for Zn-air batteries, CoFe-NC-OAc achieve high peak power densities of 193 mW cm and 587 mW cm in liquid and solid-state Zn-air batteries. The liquid battery also exhibits high specific capacity and remarkable cycling performance. This work opens up a new opportunity for developing highly efficient bifunctional electrocatalysts for Zn-air battery applications.