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

Ruthenium pyrochlores, that is, oxides of composition A₂Ru₂O_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_1.8M_0.2Ru₂O_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 phases and the coupling between the M d states and O 2p states. Our work introduces a novel catalyst with improved OER performance, Y_1.8Cu_0.2Ru₂O_7-δ, and provides general guidelines for the design of active electrocatalysts.