Ni-doping optimized d-band center in bifunctional FeO modified by bamboo-like NCNTs as a cathode material for Zn-air batteries.

During the development of Zn-air batteries, designing an affordable, efficient and stable electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) presents a great challenge. FeO exhibits ORR and OER activities, but when used as a cathode material in Zn-air batteries, its activity requires further improvement. To achieve this goal, Ni is doped into FeO hexagonal nanorods, derived from a metal-organic framework (MOF) precursor, and further modified by N-doped carbon nanotubes. In ORR, its half-wave potential achieves 0.946 and 0.716 V in alkaline and neutral electrolytes, respectively. In OER, it requires 388 mV to obtain 10 mA cm in an alkaline electrolyte. As illustrated by theoretical calculation, Ni-doping raises the d-band center of FeO, which enhances its adsorption towards relevant oxygen species in electrocatalysis. This improves its ORR and OER activities. Based on these merits, the Zn-air battery is assembled with an alkaline electrolyte. At 10 mA cm, its specific capacity and energy density reach 819.8 mA h g and 960.1 W h kg, respectively. This battery remains stable after a long time of charge and discharge. In neutral electrolytes, its promising discharge performance is also well retained. This work develops an effective approach to improve ORR and OER activities of FeO-based cathode materials in Zn-air batteries.