Recent Advances in Low-Cost, Highly Efficient Bi-Functional Oxygen Electrocatalysts for High-Performance Zinc-Air Batteries

Abstract

Zn-air batteries (ZABs) have attracted much attention for possible applications in portable electronics and electric vehicles because of several advantages such as low cost, excellent safety, and high energy density (ca. 1,084 Wh kg–1) in alkaline media. However, the development of ZABs has been hampered by low working voltage due to the sluggish rate of oxygen reduction reaction (ORR) and short lifespan under deep discharge conditions (over 30%) due to poor durability of the air electrode associated with limited stability of ORR and oxygen evolution reaction (OER) electrocatalysts. Thus, platinum group metals (e.g., Pt and Ir-based alloys) have been widely used for ORR and OER electrocatalysts, respectively. However, these materials not only are expensive but also show poor durability in practical ZABs. In this presentation, we will report some latest advances in the development of low-cost, highly efficient bi-functional oxygen electrocatalysts for ZABs. In particular, we will highlight a composite catalyst consisting of Ni46Co40Fe14 nanoparticles (with a size distribution of 30~60 nm) dispersed in a carbon matrix (denoted as C@NCF-900), produced via supercritical reaction and subsequent heat treatment at 900 °C. Among all the transition metal-based electrocatalysts, the C@NCF-900 exhibits the highest ORR performance in terms of half-wave potential (0.93 V) in 0.1 M KOH. Furthermore, C@NCF-900 exhibits negligible activity decay after 10,000 voltage cycles with minor reduction of half-wave potential (0.006 V). When evaluated in ZABs, the C@NCF-900 outperforms the mixture of 20 wt% Pt/C and IrO2, cycled over 100 h under 58 % depth of discharge condition. Furthermore, a plausible ORR/OER mechanism of C@NCF-900 is elucidated by density functional theory calculations and confirmed by operando X-ray absorption spectroscopy.