Iridium(111), Iridium(110), and Ruthenium(0001) Single Crystals as Model Catalysts for the Oxygen Evolution Reaction: Insights into the Electrochemical Oxide Formation and Electrocatalytic Activity

We report a comparative study on the influence of generic electrochemical activation-oxidation protocols on the resulting surface oxides of Ir(111) and (110) and Ru(0001) single crystals and their electrocatalytic reactivity for the oxygen evolution reaction. Well-defined single-crystal electrodes were prepared in a custom-made chamber that combines inductive thermal annealing and electrochemistry. The clean surfaces were analyzed for their electrocatalytic oxygen evolution activities and oxidation behavior. Three different oxidation protocols were used, which revealed a strong activity dependence on the duration and upper potential limit of the electrochemical oxidation. The resulting changes of the surface were followed by using cyclic voltammetry and impedance spectroscopy. Important differences between the two faces of Ir in terms of surface morphology of the formed oxide were identified, which allowed us to draw conclusions for preferable crystal faces in nanoparticle catalysts.