LAUSR

The fundamental steps and active sites in the oxygen reduction reaction (ORR) on reducible oxide surfaces is an outstanding fundamental problem in heterogeneous catalysis. For many applications, such as fuel cells, the oxygen exchange reaction is often the rate limiting step and it is critical to develop an atomic level fundamental understanding of the reaction pathways. Reducible oxides such as CeO2 (ceria) are ideal model systems to investigate the oxygen exchange reaction. Under reducing conditions, ceria releases oxygen through the formation of an oxygen vacancy coupled with a transition from Ce to Ce [1]. The ORR takes place when reduced ceria is exposed to an oxidizing environment. High-resolution transmission electron microscopy (HRTEM) has been used to study Ce atomic movement on ceria nanoparticle surfaces [2]. Recently, atomic surface structures of CeO2 cubes with O atoms clearly visible were imaged using aberration-corrected HRTEM [3]. Although performing HRTEM imaging of CeO2 under high vacuum conditions at room temperature provides valuable insights, the catalytically important applications of ceria occur at elevated temperatures in gaseous environments. In situ environmental transmission electron microscopy (ETEM) can be used to observe dynamical processes that occur on ceria surfaces in reducing/oxidizing environments at elevated temperatures. Observing oxygen surface dynamics on CeO2 will provide information on the fundamentals of the oxygen exchange reaction that is crucial for catalysis. Here we show dynamic changes on ceria related to oxygen exchange at the surface.