Electronic structure of IrO₂: The role of the metal d orbitals

IrO₂ is one of the most active catalysts for the oxygen evolution reaction (OER) and remains the only known stable OER catalyst in acidic conditions. As a first step in understanding the mechanism for OER we carried out detailed Density Functional Theory (DFT) studies of the electronic structure of IrO₂. We compared the electronic states and magnetic properties of IrO₂ using several density functionals. We found that DFT with hybrid functionals (B3PW and PBE0) leads to a weak ferromagnetic coupling, although IrO₂ has often been reported as nonmagnetic. We also found a magnetic ground state for RuO₂, whose electronic structure is similar to that of IrO₂. Ru-Ru antiferromagnetic interaction has been observed experimentally in nanoparticle RuO₂. Further low temperature measurements are necessary to confirm whether a weak magnetism may occur below 20 K in IrO₂. We also found that PBE leads to a better agreement with the experimental XPS spectra, compared with hybrid functionals and PBE+U.