Elucidating the Adsorption and Co-adsorption of Potassium and Oxygen on (110) MnO₂, TiO₂ and VO₂ Surfaces

Materials Modelling Centre, Editorial Department, University of Limpopo, Private Bag X1106, Sovenga, South Africa.

^* Corresponding author: khomotso.maentja@gmail.com

Abstract

In metal air battery, oxygen reacts with lithium ions on the cathode side of the cell which makes it much lighter than conventional cathodes used in Li-ion batteries. Density functional theory (DFT) study is employed in order to investigate the surfaces of, (Rutile) R-MnO₂, TiO₂ and VO₂ (MO₂), which act as catalysts in metal-air batteries. Adsorption and co-adsorption of metal K and oxygen on (110) β-MO₂ surface is investigated, which is important in the discharging and charging of K- air batteries. Only five values of (gamma) are possible due to the size of the supercell and assuming that oxygen atoms occupy bulk-like positions around the surface metal atoms. The manganyl, titanyl and vanadyl terminated surface are not the only surfaces that can be formed with Γ= +2, oxygen can be adsorbed also as peroxo species (O₂)^2-, with less electron transfer from the surface vanadium atoms to the adatoms than in the case of manganyl, titanyl or vanadyl formation. MnO₂ promotes formation of KO₂ for all configurations whereas TiO₂ partially promote nucleation of KO₂ whereas VO₂ surfaces form very stable KO₂ clusters, thus VO₂ is not a good catalyst for the formation of KO₂. The fundamental challenge that limits the use of metal air battery technology, however, is the ability to find a catalyst that will promote the formation and decomposition of discharge products during the charging and discharging cycle, i.e. oxygen reduction reaction (ORR) and oxygen evolution reaction (OER).