Electronic Structure of IrO_2: The Role of the Metal d Orbitals

Abstract

IrO_2 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 IrO_2. We compared the electronic states and magnetic properties of IrO_2 using several density functionals. We found that DFT with hybrid functionals (B3PW and PBE0) leads to a weak ferromagnetic coupling, although IrO_2 has often been reported as nonmagnetic. We also found a magnetic ground state for RuO_2, whose electronic structure is similar to that of IrO_2. Ru–Ru antiferromagnetic interaction has been observed experimentally in nanoparticle RuO_2. Further low temperature measurements are necessary to confirm whether a weak magnetism may occur below 20 K in IrO_2. We also found that PBE leads to a better agreement with the experimental XPS spectra, compared with hybrid functionals and PBE+U.

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