Composition and electronic structure of Mn3O4 and Co3O4 cathodes in zinc/air batteries: a DFT study

The surface structures of promising cathode materials for zinc-air batteries, Mn3O4 and Co3O4, have been systematically studied under operating conditions by density functional theory calculations. The environment has been taken into account using grand-canonical schemes both for gas-phase and electrochemical conditions. By analysing the structures appearing in the calculated phase diagrams and Pourbaix diagrams in detail, we derive the factors underlying their stability in the gas phase and under electrochemical conditions. Changes in charge, oxidation states and spin states of the metal cations on the surface are discussed and their feasibility as active centers for the oxygen evolution and reduction reaction is thoroughly analyzed.