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

We have synthesized metal oxides (MnO 2 , RuO 2 , IrO 2 , 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 MnO 2 , RuO 2 and IrO 2 . The samples showed stable performance in terms of their overpotential. The MnO 2 -based metal oxide exhibited a relatively lower overpotential for ORR. Mn 1-n Ru n O x , Ru 1-n Ni n O x , and Ru 1-n Ir n O x were identified as preferable catalysts for OER. From the samples examined in this study, Mn 1-n Ru n O x (n = 0.1, 0.2, 0.8) and Ru 0.9 Ni 0.1 O x showed promise as bifunctional catalysts.