Electrocatalytic Oxygen Reduction and Water-Oxidation on Transition Metal Ion-Doped MnO₂, RuO₂ and IrO₂ in Alkaline Aqueous Solutions

We have synthesized metal oxides (MnO₂, RuO₂, IrO₂, and transition metal (Ru, Ir and Ni) ion-doped metal oxides) using a precipitation method and exhaustively examined their bifunctional electrocatalytic activities for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline solutions. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements were used to study the structure and electronic states of the catalysts. The XRD and XPS data confirmed the successive modification of the structure and electronic states on the catalyst surface by doping transition metal ions into MnO₂, RuO₂ and IrO₂. The samples showed stable performance in terms of their overpotential. The MnO₂-based metal oxide exhibited a relatively lower overpotential for ORR. Mn_1-nRu_nO_x, Ru_1-nNi_nO_x, and Ru_1-nIr_nO_x were identified as preferable catalysts for OER. From the samples examined in this study, Mn_1-nRu_nO_x (n = 0.1, 0.2, 0.8) and Ru_0.9Ni_0.1O_x showed promise as bifunctional catalysts.