Rationalizing Effect of Metal Substitution in Ruthenium Pyrochlores on the Lattice Oxygen Binding and Oxygen Evolution Activity

Abstract

Ruthenium pyrochlores, i.e. oxides of composition A2Ru2O7 − δ, are known as advanced catalysts for the oxygen evolution reaction (OER) in acidic conditions.1 In this work, we discuss a direct correlation between the OER activity of Y1.8M0.2Ru2O7 − δ pyrochlores (M = Y, Fe, Co, Ni, Cu), the lattice oxygen binding strength/lability and the formation enthalpy of the binary MOx oxide, i.e. metals M with highter enthalpies of formation for the respective oxide weaken the oxygen binding on the surface of Y1.8M0.2Ru2O7 − δ pyrochlores that results in enhanced OER activity. DFT studies captured changes in the electronic structure of the Y1.8M0.2Ru2O7 − δ oxides induced by M substitution and revealed trends in the electronic band structure that govern the OER performance of the Y1.8M0.2Ru2O7 − δ catalysts. Specifically, an increase in the density of oxygen vacancy (VO) sites and the OER activity in Y1.8M0.2Ru2O7 − δ is attributed to the shift of the O 2p band center closer to the Fermi level. Our work introduces Y1.8Cu0.2Ru2O7 − δ as a novel OER catalyst with enhanced OER activity and, more fundamentally, emphasizes the underexplored role that substituents can play in regulating the OER activity of complex oxides, i.e. by influencing the surface oxygen binding strength. Our results can be utilized for the rational design of new compositions for oxygen electrocatalysis and other applications that involve lattice oxygen sites.(1) Kim, J.; Shih, P.-C.; Tsao, K.-C.; Pan, Y.-T.; Yin, X.; Sun, C.-J.; Yang, H., J. Am. Chem. Soc. 2017, 139, 12076-12083.