DFT Studies of Catalytic Activity of Rutile Typed Metal Oxide (110) Surface in Sodium-Air Batteries

Abstract

Metal-air batteries, such as Li-air, have been extensively studied owing to their high theoretical energy density, which is up to three times that of the conventional to Li-ion batteries and interest in Na-air is now emerging [1,2, 3]. The current study is providing a better understanding of the catalytic activity of rutile typed MO2 (MnO2, TiO2 and VO2) for the oxygen reduction and oxygen evolution reactions in Na-air batteries, using density functional methods. When oxygen is adsorbed at the Na/MO2 (110) surface different clusters, such as superoxide, peroxo on Na/M, and dissociated configurations are formed. Our current study has demonstrated that MnO2, as a catalyst, promotes nucleation and growth of both Na2O and Na2O2. On the contrary, other metal oxides such as TiO2 and VO2 do not depict this catalytic effect towards the formation of discharge products in Na-O2 batteries. Furthermore, it can be deduced from our calculated electronic properties, in the form of an intercept of the density of states (DOS) by the Fermi level, that Mn catalyzed configurations are more stable than those based on Ti and V. It can therefore be surmised that the MnO2 catalyst supports the formation of NaO2 which is the most stable discharge product in Na-air batteries. Furthermore, the surface NaO2 appears to have bond lengths comparable to those of the bulk and monomer NaO2.