Oxidized Overlayers of Ruthenium and Iridium as Electrocatalysts for Anodic Reactions

Renewable energy technologies often rely on rutile tetravalent oxides, such as ruthenium(IV) oxide and iridium(IV) oxide, to catalyze anodic reactions that are paired with fuel formation. Herein, we report the synthesis of angstrom-scale and nanoscale oxidized overlayers of ruthenium (o-RuO_<i>x</i>) and iridium (o-IrO_<i>x</i>) from simple aqueous precursors grown on earth-abundant supports and state-of-the-art oxide electrocatalysts. The resulting overlayers exhibit distinct redox features and chemical states as indicated by cyclic voltammetry, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. The electrocatalysts exhibit increased activity towards anodic reactions. In particular, annealed o-RuO_<i>x</i> grown on TiO₂ (a-TiO₂/o-RuO_<i>x</i>) results in an electrocatalyst with an overpotential of 213, 206, and 14 mV at 10 mA cm^-2 for the oxygen evolution reaction (OER) in acid, the OER in base, and the chlorine evolution reaction, respectively. The activity of a-TiO₂/o-RuO_<i>x</i> corresponds to a 47.7×, 117.4×, and 1.3× increase in ruthenium mass activity compared to RuO₂ towards the OER in acid, the OER in base, and the chlorine evolution reaction, respectively. These findings highlight the unique chemistry of oxidized overlayers and their potential to meet operational demands for renewable energy technologies.