Short Term Silver Electrode Microstructure Changes Under Epoxidation Conditions for Solid Oxide Electrolysis Cells

Abstract

Ethylene epoxidation is an important reaction forming ethylene oxide (EO), which is a precursor to many other critical chemicals. This study links short-term EO production to the effects on the microstructure of Ag/yttria-stabilized zirconia cells with and without electrochemical promotion of catalysis (EPOC). Nano-scale features, called striations, were observed on the silver under all epoxidation reaction conditions tested, using a scanning electron microscope. While appearing in both cases, the striations for the EPOC case are finer in size (~150 to 250 nm) compared to the no current case (~400 to 500 nm). These features did not appear when epoxidation conditions were not present. Striation formation was further linked to the epoxidation reaction through electrochemical impedance spectroscopy and gas chromatography. Ethylene conversion to EO declines over the course of hours as striations form, indicating that striations have a negative influence on the reaction. Distribution of relaxation times was performed to determine the effect striation formation has on the electrochemical performance of the cells. It was observed that the low-frequency peaks in the DRT analysis significantly decrease as striations formed over the course of 10 hours.