Electrochemical characterization of electrolyte supported solid oxide electrolysis cell during CO2/H2O co-electrolysis.

High-temperature co-electrolysis is studied on electrolyte-supported NiO-YSZ/NiO-SDC/ScSZ/LSCF-GDC/LSCF (NiO: Nickel Oxide, YSZ: Yttria-stabilized zirconia, SDC: Samarium-doped ceria, ScSZ: Scandia-stabilized zirconia, LSCF: Lanthanum Strontium Cobalt Ferrite, GDC: Gadolinium-doped ceria) button cell. Electrochemical impedance spectroscopy (EIS) was recorded under open-circuit voltage (OCV) and co-electrolysis mode over various operating conditions, including temperature, water vapor content, and applied voltage. Interfacial polarization resistance (Rp) is obtained from peak arcs located in the three regions: gas conversion resistance (Region I (0.01 to 0.1 Hz)), gas diffusion resistance (Region II (0.1 to 100 Hz)) and air electrode charge transfer resistance (Region III (100 to 10,000 Hz)). As the temperature increased from 700 to 850 oC, Rp decreased from 18.15 to 3.32 Ω.cm2 at 1.3 V for 10%CO2/3%H2O. From the Distribution of relaxation times (DRT) studies, one additional peak, P5 (fuel gas conversion or gas-phase diffusion in the pores of the air electrode), is observed, and Region III (100 to 10,000 Hz) consists of two additional peaks: P1 (ionic transport coupled with gas diffusion close to triple phase boundaries (TPBs)) and P2 (fuel electrode charge transfer reaction), which were not clearly distinguished from EIS. Region II dominates in the overall polarization resistance. At 800 oC, for 10%CO2/3%H2O, the Rp decreased from 6.78 to 4.82 Ω.cm2, with an increase in the applied voltage from 1.3 to 1.5 V. At 800oC/1.5 V, the Rp values are 4.41, 8.09, and 6.77 Ω.cm2 for H2O, CO2, and co-electrolysis. At 800 ºC/1.5 V, with an increase in the water vapor content from 3%H2O to 15%H2O, there is not much change in the Rp value; therefore, 10%H2O is sufficient. H2 consumption is between 23 and 36%, depending on the temperature at OCV. At 800 °C for (10%H2/10%CO2/10%H2O), co-electrolysis occurs at applied voltage, along with Reverse water gas shift (RWGS) reaction. [ABSTRACT FROM AUTHOR]