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

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., RuO 2 and IrO 2 ). Recently, ternary compounds have been reported to have excellent OER performance. Among them, our group developed pyrochlore-type electrocatalysts of various compositions. Yttrium ruthenate (Y 2 Ru 2 O 7-δ ) was shown to have significantly enhanced performance towards OER in acid media over both RuO 2 and IrO 2 catalysts at current density about 1 mA/cm 2 [1]. It has an onset overpotential of 190 mV in 0.1-M perchloric acid solution. Tafel plots show the Y 2 Ru 2 O 7-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 RuO 2 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 (Y 2 Ru 2 O 7-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 A 2 Ru 2 O 7-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]. References: M. Kim, # P.-C. Shih, # K.-C. Tsao, Y.-T. Pan, X. Yin, C.-J. Sun, H. Yang, J. Am. Chem. Soc ., 2017 , 139 , 12076-12083 (#: equal contribution). M. Kim, X. X. Chen, Y.-T. Pan, P.-C. Shih, H. Yang, J. Electrochem. Soc ., 2017 , 164 , F1074-F1080. M. Kim, X. X. Chen, P.-C. Shih, H. Yang, ACS Sustainable Chem. Eng. , 2017 , 5 , 10190-10917.