Iridium–ruthenium single phase mixed oxides for oxygen evolution: Composition dependence of electrocatalytic activity

Abstract

► Solid solutions of iridium oxide and ruthenium oxides were produced hydrothermally. ► Iridium segregates to the surface. ► The electrocatalytic activity for oxygen evolution for the solid solutions was the same as for physically mixed iridium and ruthenium oxides. Mixed iridium–ruthenium oxide is a promising electrocatalyst for the oxygen evolution reaction. The interaction of the two elements and their contribution to the catalytic activity are of fundamental interest. An iridium–ruthenium oxide catalyst was therefore prepared hydrothermally and characterised by cyclic voltammetry, steady state polarisation measurements, X-ray diffraction and X-ray photoelectron spectroscopy. The catalysts were shown to be solid solutions. Due to significant surface segregation of IrO 2 the range of surface compositions was much narrower than the bulk composition-range. The charge-normalised current densities at constant potential for these surface-segregated solid solutions were found to be similar to those obtained at catalysts prepared by physically mixing corresponding ratios of the end-member oxides IrO 2 and RuO 2 . Tafel slopes were in the order of 40 mV dec −1 for the end members and slightly higher for intermediate compositions.