Formation and Nucleation of Discharge Products in Metal-air Batteries Supported by Metal oxide Catalysts

Catalytic effect on the performance of metal air battery has been intensively studied for Li-air battery whereas, not much focus has been given to Na-air batteries yet. However, it has been reported that the most stable product in Na-air battery is NaO₂ whereas in Li-air battery it has been reported that the major and stable product is Li₂O₂. In this work, we present density functional theory study of how metal oxide (MnO₂, TiO₂ and VO₂) catalyst affects nucleation of Li₂O₂ and NaO₂ and other products that may be formed. We further investigate the discharge products of these two metal air batteries compared to the known systems of the product in terms of their formation energy and their morphology. Interestingly it has been found that what was reported in literature, that the most stable products in Na-air batteries being NaO₂ is indeed what has been observed in our study. Furthermore, the type of structure that has been found was the pyrite form whereas the most stable product in Li-air battery, Li₂O₂ has the hexagonal type. Amongst the three metal oxides, MnO₂, is the most efficient catalyst because it encourages the formation of the reported stable products in both Li and Na air batteries.