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

Abstract

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.