Three-dimensional interconnected core-shell networks with Ni(Fe)OOH and M-N-C active species together as high-efficiency oxygen catalysts for rechargeable Zn-air batteries

NiFe alloys and metal-nitrogen-carbon materials (M-N-C, M = Ni, Fe, Co, etc.) are foremost catalysts in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) process, respectively. Nevertheless, the monotonic performance and insufficient stability hinder their practical application in rechargeable batteries. Herein, we simultaneously combine Ni(Fe)OOH and Ni/Fe-N-C active sites together into 3D interconnected core-shell nanochains (Ni2Fe1@PANI-KOH900). The obtained catalyst exhibits robust activity and durability in both OER and ORR reactions with a startlingly low overpotential of 240 mV at a current density of 10 mA cm(-2) (E-j=10 = 1.47 V vs. RHE) and a more positive half-wave potential (E-1/2 = 0.92 V vs. RHE), superior to those of the benchmark RuO2 and Pt/C catalysts. The potential gap (Delta E = E-j=10 - E-1/2) is merely 0.55 V. Intensive investigations through in situ confocal Raman and HTEM-HAADF techniques indicate that the Ni(Fe)OOH and Ni/Fe-N-C active species as well as the unique 3D interconnected network-like structure are responsible for the state-of-the-art OER and ORR performances. Furthermore, the assembled rechargeable Zn-air battery comprising Ni2Fe1@PANI-KOH900 exhibits unprecedented superior charging-discharging performance and durable cycle life, holding great potential for energy conversion and storage devices.