In Situ Optical Studies of CO2 and Co-Electrolysis

Abstract

The ability to understand the underlying mechanisms for electrolysis of CO2 and co-electrolysis of CO2 and steam has been hindered due to a lack of experimental methods that can probe intermediate species and materials directly during operation. Although there have been studies on using Ni-YSZ and ceria based cathodes for electrode materials in high temperature solid oxide electrolysis cells (SOECs), these have mainly utilized post-mortem and in situ electrochemical analyses. Here, we demonstrate an in situ duplex technique that combines near infrared thermal imaging (NIRTI) and Fourier-transform infrared emission spectroscopy (FTIRES) to monitor processes for electrolysis of CO2 and co-electrolysis on operating SOECs. The results are correlated with traditional electrochemical measurements to identify any polarization dependence on species during the course of reactions under a range of conditions. CO2 and co-electrolysis conditions are investigated on anode- and electrolyte-supported cells between 700 and 900 °C. NIRTI results indicate cooling on the anode surface during endothermic processes and heating during high loads due to joule heating. FTIRES indicates the first observation of a carbonate intermediate formed on a cathode during operation at normal SOEC working pressure and temperature. Diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) is used to confirm band assignments seen in situ for electrode materials. Ex situ mass spectrometry and exhaust gas FTIR absorption measurements are combined with in situ results to further characterize and quantify carbon monoxide and syn-gas production. These studies serve as benchmark data for better understanding the processes during CO2 electrolysis in real working conditions.