Functionalizing Titanium Disilicide Nanonets with Cobalt Oxide and Palladium for Stable Li Oxygen Battery Operations

Li oxygen (Li-O2) batteries promise high energy densities but suffer from challenges such as poor cycling lifetime and low round-trip efficiencies. Recently, the instability of carbon cathode support has been recognized to contribute significantly to the problems faced by Li-O2 batteries. One strategy to address the challenge is to replace carbon materials with carbon-free ones. Here, we present titanium silicide nanonets (TiSi2) as such a new material platform for this purpose. Because TiSi2 exhibits no oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) activities, catalysts are required to promote discharge and recharge reactions at reduced overpotentials. Pd nanoparticles grown by atomic layer deposition (ALD) were observed to provide the bifunctionalities of ORR and OER. Their adhesion to TiSi2 nanonets, however, was found to be poor, leading to drastic performance decay due to Pd detachments and aggregation. The problem was solved by adding another layer of Co3O4, also prepared by ALD. Together, the Pd/Co3O4/TiSi2 combination affords the desired functionalities and stability. Li-O2 test cells that lasted more than 126 cycles were achieved. The reversible formation and decomposition of Li2O2 was verified by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), ferrocenium back-titration, and gas-chromatography and mass spectrometry (GC-MS). Our results provide a new material platform for detailed studies of Li-O2 operations for better understanding of the chemistries involved, which is expected to help pave the way toward practical Li-O2 battery realizations.