Tailoring Lattice Oxygen Binding in Ruthenium Pyrochlores to Enhance Oxygen Evolution Activity.

Ruthenium pyrochlores, that is, oxides of composition A ₂ Ru ₂ O _7-δ , have emerged recently as state-of-the-art catalysts for the oxygen evolution reaction (OER) in acidic conditions. Here, we demonstrate that the A-site substituent in yttrium ruthenium pyrochlores Y _1.8 M _0.2 Ru ₂ O _7-δ (M = Cu, Co, Ni, Fe, Y) controls the concentration of surface oxygen vacancies (V _O ) in these materials whereby an increased concentration of V _O sites correlates with a superior OER activity. DFT calculations rationalize these experimental trends demonstrating that the higher OER activity and V _O surface density originate from a weakened strength of the M-O bond, scaling with the formation enthalpy of the respective MO _x phases and the coupling between the M d states and O 2 p states. Our work introduces a novel catalyst with improved OER performance, Y _1.8 Cu _0.2 Ru ₂ O _7-δ , and provides general guidelines for the design of active electrocatalysts.