Prediction of Ir0.5M0.5O2 (M = Cr, Ru or Pb) Mixed Oxides as Active Catalysts for Oxygen Evolution Reaction from First-Principles Calculations

Hydrogen generation via water splitting suffers from a substantial energy loss mainly due to the sluggish oxygen evolution reaction (OER) at anode. The noble metal oxide, such as iridium dioxide (IrO2), is considered as a promising oxygen-evolving catalyst in proton exchange membrane based electrolysis cell, though it still needs to be improved due to the large over-potential. At the same time, composite materials containing lower amount of Ir without appreciable loss in electrocatalytic activity are also in high demand. By using the first-principles density functional theory calculations, we have studied the OER at IrO2 substituted with M (Ti, Cr, Mn, Ru, Rh, Pt, Sn, Pb) to search for the candidate catalysts with lower over-potential. Our calculation results show that the formation of Ir0.5Ti0.5O2 solid solution is thermodynamically the easiest and Pt cation is the most difficult to be substituted into IrO2 lattice. When OER occurs, the surfaces for pure and doped IrO2 are readily covered with O. The formation of adsorbed HOO at Ir0.5M0.5O2 catalysts is the potential-determining step which gives the theoretical over-potential close to that of pure IrO2. The free energy changes of this step increase in doped IrO2 systems with Ti, Mn, Rh, Pt or Sn, while they reduce at Ir0.5Cr0.5O2, Ir0.5Ru0.5O2 and Ir0.5Pb0.5O2 catalysts. In particular, compared to the pure IrO2, the binding strength of O is weakened more significantly than that of HOO at the Cr-, Ru- and Pb-doped IrO2, leading to the reduction of the free energy differences.