(Invited) Pyrochlore-Type, Acid-Stable Electrocatalysts for Oxygen Evolution Reaction

Abstract

Multiple important electrochemical processes including hydrogen generation from water reply on acid-stable electrocatalysts for oxygen evolution reaction (OER). The material choice of OER electrocatalysts in acid is often limited to only two major types of oxides (e.g., RuO2 and IrO2). Recently, ternary compounds have been reported to have excellent OER performance. Among them, our group developed pyrochlore-type electrocatalysts of various compositions. Yttrium ruthenate (Y2Ru2O7-δ) was shown to have significantly enhanced performance towards OER in acid media over both RuO2 and IrO2 catalysts at current density about 1 mA/cm2 [1]. It has an onset overpotential of 190 mV in 0.1-M perchloric acid solution. Tafel plots show the Y2Ru2O7-δ catalyst had enhanced activity from 55 mV/dec for the first cycle to 46 mV/dec for the 10,000th cycle. In comparison, the OER performance for RuO2 catalyst degraded from 61 mV/dec for the first cycle to 72 mV/dec for the 10,000th cycle under the same testing conditions. A range of techniques including X-ray absorption spectroscopy (XAS) and computational tools such as density functional theory (DFT) calculation have been used to understand the structural origins of enhanced performance. Our preliminary data suggest a low valence state in yttrium ruthenate (Y2Ru2O7-δ) favors the high OER activity, while lowered band center energy for the overlap between Ru 4d and O 2p orbitals contributes to the stability. A systematic study on the structural origin for high OER performance has further been carried out using a series of A2Ru2O7-δ pyrochlore-type electrocatalysts and will be presented in this talk. Strategies for improving the overall performance of these OER catalysts will also be discussed [2,3].