Impact of Surface Chemistry on the Electrochemical Performance of Perovskite Cathodes

Surface chemistry and reactivity of electrodes in electrochemical devices play a key role for electrochemical performance and cell durability. In this work, we use spatially resolved scanning photoelectron microscopy and electrochemical measurements to study in situ the surface chemistry of perovskite catalysts in SOFC cathode model cells during high temperature operation at 500-550°C in oxygen containing environment (10-6mbar) at OCV or under oxygen flux. Oxygen ion flux and electric field cause dynamic changes of catalyst and electrolyte surface chemistry, including redox reaction, surface segregation and long range surface diffusion. In (La,Sr)Mn1+xO3-δ (LSM) cathodes, oxidizing environment was found to promote transition metal-rich cathode surface termination with high surface oxygen content and a variety of oxygen surface species, while reducing environment produced surface segregation of strontium and low level of surface oxygen. The electrochemical response provided the rate-determining reaction steps of the operating model cell and could directly be compared to the spectroscopic observations