Fe-FeOx nanoparticles anchored on nitrogen-doped carbon support : a robust bifunctional catalyst for zinc-air batteries

Abstract

Developing bifunctional electrocatalysts with exceptional activity and stability for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for advancing zinc-air batteries (ZABs). However, the prohibitive cost of precious metal catalysts and the challenge of optimizing bifunctionality in non-precious alternatives remain significant hurdles. This study innovatively synthesizes Fe-FeOₓ nanoparticles anchored on nitrogen-doped carbon (Fe-FeOₓ/NC) by coupling flash nanoprecipitation (FNP) with a carbon bath method (CBM). FNP dramatically reduces the metal-organic framework (MOF) synthesis time, offering a pathway for continuous production, and subsequent CBM yields the Fe-FeOₓ/NC catalyst. Remarkably, this catalyst exhibits outstanding bifunctional electrocatalytic performance in alkaline media, evidenced by the potential gap (ΔE = E<inf>j=10</inf>-E<inf>1/2</inf>) of 0.705 V. Through in-depth in-suit characterization and theoretical calculations, we elucidate the origin of its high activity: OER activity primarily stems from the Fe site within the oxide, while ORR activity originates from C-N<inf>x</inf> (C) site. Notably, ZABs employing Fe-FeO<inf>x</inf>/NC demonstrate a high specific capacity of 719 mAh·g<inf>Zn</inf>−1, and exceptional cycling stability exceeding 400 h. This work not only presents a high-performance catalyst but also provides novel insights into the synergistic role of distinct active sites, guiding the design of advanced oxygen electrocatalysts.