Double Coating of Iron-Containing Carbonaceous Thin Film for Enhanced Bifunctional Catalysis for Use in Air Electrodes

Abstract

Bifunctional catalysts for oxygen reduction and evolution reactions are essential components of zinc–air batteries (ZABs) for the air electrode. Carbonaceous materials have been investigated as these catalysts since the early stage of ZAB research. Recent studies have revealed promising carbonaceous materials with heteroatoms and transition metals doped into the surface or incorporated as nanoparticles, although the activity still needs improvement. In this study, the double coating of carbonaceous thin film containing Fe and N on a graphitic carbon fiber surface was performed via sublimation, deposition, and pyrolysis of iron phthalocyanine (FePc). In the first coating, the thin film and Fe nano-aggregates on the surface were generated, which were encapsulated in the carbonaceous shell to generate protrusions in the second coating. The presence of the protrusion enhanced the oxygen reduction activity. Such protrusion was also formed by the single coating with a sufficient FePc feed; however, the activity enhancement was limited. Contrarily, the double coating considerably enhanced the activity and surpassed that of Pt in the high potential region. In addition, the oxygen evolution reaction was improved by the FePc-derived thin film coating. The durability was confirmed by the stable cycling performance of ZAB with the double-coated electrode.