Atomic Layer Deposited Non-Noble Metal Oxide Catalyst for Sodium-Air Batteries: Tuning the Morphologies and Compositions of Discharge Product

Catalysts can play a critical role in the development of sodium-air batteries (SABs). Atomic layer deposition (ALD) technology enables rational design and atomic utilization of catalyst by homogenously distributing catalytically active material on a variety of substrates. Here, a novel hierarchical nanostructured Co3O4 is decorated on carbon nanotubes by ALD (CNT@ Co3O4) and used as a catalyst for SABs. CNT@ Co3O4 demonstrates better performance and longer cycle life than a mechanically mixed CNT/Co3O4 nanocomposite. Well-dispersed ALD Co3O4 catalyst on CNTs, which serves as functionalized active sites, enables rapid electron exchange and high oxygen reduction/evolution activities. Synchrotron-based X-ray analysis including X-ray absorption near edge structure, extended X-ray absorption fine structure, and scanning transmission X-ray microscopy characterization techniques have been employed to elucidate the activity of Co3O4 and to investigate the nanoscale discharge product distribution found in SABs. This analysis reveals that Co3O4 catalyst can promote the electrochemical decomposition of sodium peroxide, superoxide, and carbonates. The role of the catalyst in SABs is clarified and discussed in detail.