Ni-doping optimized d-band center in bifunctional Fe2O3 modified by bamboo-like NCNTs as a cathode material for Zn-air batteries.

Abstract

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. Fe2O3 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 Fe2O3 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-2 in an alkaline electrolyte. As illustrated by theoretical calculation, Ni-doping raises the d-band center of Fe2O3, 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-2, its specific capacity and energy density reach 819.8 mA h g-1 and 960.1 W h kg-1, 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 Fe2O3-based cathode materials in Zn-air batteries.