Lewis Acid Site Assisted Bifunctional Activity of Tin Doped Gallium Oxide and Its Application in Rechargeable Zn-Air Batteries.

The enhanced safety, superior energy, and power density of rechargeable metal-air batteries make them ideal energy storage systems for application in energy grids and electric vehicles. However, the absence of a cost-effective and stable bifunctional catalyst that can replace expensive platinum (Pt)-based catalyst to promote oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air cathode hinders their broader adaptation. Here, it is demonstrated that Tin (Sn) doped β-gallium oxide (β-Ga 2 O 3 ) in the bulk form can efficiently catalyze ORR and OER and, hence, be applied as the cathode in Zn-air batteries. The Sn-doped β-Ga 2 O 3 sample with 15% Sn (Sn x =0.15 -Ga 2 O 3 ) displayed exceptional catalytic activity for a bulk, non-noble metal-based catalyst. When used as a cathode, the excellent electrocatalytic bifunctional activity of Sn x =0.15 -Ga 2 O 3 leads to a prototype Zn-air battery with a high-power density of 138 mW cm -2 and improved cycling stability compared to devices with benchmark Pt-based cathode. The combined experimental and theoretical exploration revealed that the Lewis acid sites in β-Ga 2 O 3 aid in regulating the electron density distribution on the Sn-doped sites, optimize the adsorption energies of reaction intermediates, and facilitate the formation of critical reaction intermediate (O*), leading to enhanced electrocatalytic activity.