Targeted design of α-MnO₂ based catalysts for oxygen reduction

The paper focuses on theoretical and experimental aspects of an oxide surface optimization for oxygen reduction reaction (ORR). Various doped α-MnO₂ based electrocatalysts were prepared by microwave-assisted hydrothermal synthesis and electrochemically characterized to validate density functional theory (DFT) based predictions of the oxidation state and local structure effects on the catalytic activity of α-MnO₂ catalysts in ORR. Both theory and experiments conclude that the highest activity in ORR is to be expected in the case of clustered Mn³⁺ sites which yield activity comparable with that of the polycrystalline Pt. These active sites have to be formed under in-operando conditions and their formation is hindered in doped alpha-MnO₂ catalysts. The activity of the other conceivable active sites based on non-clustered Mn³⁺ or Mn⁴⁺ is inferior to that of clustered Mn³⁺. The activation of Mn³⁺ or Mn⁴⁺ based active sites leads to a shift in selectivity of the ORR process towards 2 electron formation of hydrogen peroxide.