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

Abstract

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 (R<inf>p</inf>) 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, R<inf>p</inf> decreased from 18.15 to 3.32 Ω.cm2 at 1.3 V for 10%CO<inf>2</inf>/3%H<inf>2</inf>O. From the Distribution of relaxation times (DRT) studies, one additional peak, P<inf>5</inf> (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: P<inf>1</inf> (ionic transport coupled with gas diffusion close to triple phase boundaries (TPBs)) and P<inf>2</inf> (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%CO<inf>2</inf>/3%H<inf>2</inf>O, the R<inf>p</inf> 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 R<inf>p</inf> values are 4.41, 8.09, and 6.77 Ω.cm2 for H<inf>2</inf>O, CO<inf>2</inf>, and co-electrolysis. At 800 ºC/1.5 V, with an increase in the water vapor content from 3%H<inf>2</inf>O to 15%H<inf>2</inf>O, there is not much change in the R<inf>p</inf> value; therefore, 10%H<inf>2</inf>O is sufficient. H<inf>2</inf> consumption is between 23 and 36%, depending on the temperature at OCV. At 800 °C for (10%H<inf>2</inf>/10%CO<inf>2</inf>/10%H<inf>2</inf>O), co-electrolysis occurs at applied voltage, along with Reverse water gas shift (RWGS) reaction. Graphical Abstract: (Figure presented.) © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.