A Stable Bifunctional Catalyst for Rechargeable Zinc-Air Batteries: Iron-Cobalt Nanoparticles Embedded in a Nitrogen-Doped 3D Carbon Matrix.

Low-cost, efficient bifunctional electrocatalysts are needed to mediate the oxygen reduction and oxygen evolution reactions (ORR/OER) in Zn-air batteries. Such catalysts should offer binary active sites and an ability to transfer oxygen-based species and electrons. A 3D catalyst, composed of nanoparticles of CoFe alloy embedded in N-doped carbon nanotubes tangled with reduced graphene oxide, was developed, which presents appreciable ORR/OER activity when applied in a Zn-air battery. A high open-circuit voltage of 1.43 V, a stable discharge voltage of 1.22 V, a high energy efficiency of 60.1 %, and excellent stability after 1 600 cycles at 10 mA cm-2 are demonstrated. An all-solid-state battery had an outstanding lifetime and high cell efficiency even upon bending. In situ X-ray absorption spectroscopy revealed that OOH* and O* intermediates induce variations in the Fe-Fe and Co-Co bond lengths, respectively, suggesting that Fe and Co species are crucial to the ORR/OER processes.