Visualization of oxide ion incorporation in CO2 electrolysis on LSCM-based cathodes of solid oxide electrolysis cell

In order to overcome the severe degradation of widely -used Ni-based cathodes in solid oxide electrolysis cells (SOECs), Ni-free oxide cathodes have recently attracted much attention. In this study, CO2 electrolysis mechanism at LSCM((La0.75Sr0.25)0.97Cr0.5Mn0.5O3) and LSCM/GDC (Gd-doped CeO2) porous cathodes of SOEC, which are promising oxide cathodes, is investigated through active sites imaging by oxygen isotope labeling combined with electrochemical measurements. CO2 electrolysis supplied with C18O2 and subsequent cell quenching is conducted at 1073 K using button cells with LSCM or LSCM/GDC cathodes. From the 18O distribution in the cross section of the cathodes, oxygen is incorporated into the GDC from the triple phase boundary or GDC surface for the LSCM/GDC cathode while oxygen incorporation from the LSCM surface to its bulk occurs at the LSCM cathode. The impedance spectra show that low -frequency component of the polarization resistance is approximately 5.6 times larger than high -frequency component for the LSCM/GDC whereas both components are comparative for the LSCM. These results indicate that surface processes are the dominant resistance compared to of charge transfer process in the oxygen incorporation path into GDC. In the incorporation path into LSCM, however, the both processes cause major resistances.