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

摘要

Ruthenium pyrochlores, i.e. oxides of composition A_2Ru_2O_(7-δ), are known as advanced catalysts for the oxygen evolution reaction (OER) in acidic conditions. In this work, we discuss a direct correlation between the OER activity of Y_(1.8)M_(0.2)Ru_2O_(7-δ) pyrochlores (M = Y, Fe, Co, Ni, Cu), the lattice oxygen binding strength/lability and the formation enthalpy of the binary MO_x oxide, i.e. metals M with highter enthalpies of formation for the respective oxide weaken the oxygen binding on the surface of Y_(1.8)M_(0.2)Ru_2O_(7-δ) pyrochlores that results in enhanced OER activity. DFT studies captured changes in the electronic structure of the Y_(1.8)M_(0.2)Ru_2O_(7-δ) oxides induced by M substitution and revealed trends in the electronic band structure that govern the OER performance of the Y_(1.8)M_(0.2)Ru_2O_(7-δ) catalysts. Specifically, an increase in the density of oxygen vacancy (V_O) sites and the OER activity in Y_(1.8)M_(0.2)Ru_2O_(7-δ) is attributed to the shift of the O 2p band center closer to the Fermi level. Our work introduces Y_(1.8)M_(0.2)Ru_2O_(7-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.