The Influence of Inert Ions on the Reactivity of Manganese Oxides

Artikel i vetenskaplig tidskrift, 2018

Inert ion doping is a possible method to modify electrical conductivity and catalytic activity of transition-metal oxide electrocatalysts. Despite the importance of dopants, little is known about the underlying mechanisms for the change of the system properties. We have performed density functional theory calculations to investigate the influence of different valent ions on the O 2 evolution reaction activity of β-MnO 2 and Mn 2 O 3 . While Mn 2 O 3 is unaffected by dopants, β-MnO 2 is strongly affected by ions placed in a subsurface position. Doping does not affect the ion charge at the active site, but instead it effects the bond character. This is concluded through an analysis of the density overlap regions indicator and the density of states showing that the partially covalent nature of the bonds in β-MnO 2 is responsible for the changes in the adsorbate binding energies. This mechanism is not active in the mostly ionic Mn 2 O 3 . These results highlight the need to explicitly consider the detailed bonding situation and to go beyond simple charge transfer considerations when describing doping of transition metal oxide catalysts.