Current-Voltage (i-V) characteristics of electrolyte-supported (NiO-YSZ/NiO-SDC/ScSZ/LSCF-GDC/LSCF) solid oxide electrolysis cell during CO2/H2O co-electrolysis

Abstract

Solid oxide electrolysis cells (SOECs) stabilize CO₂ emissions by converting CO₂/H₂O into synfuel. Current-Voltage (i-V) characteristics of an electrolyte-supported button cell (NiO-YSZ/NiO-SDC/ScSZ/LSCF-GDC/LSCF) were measured as a function of temperature, water vapor concentration, and CO₂ gas concentrations. The cell microstructure was characterized by the Field Emission Scanning Electron Microscope (FE-SEM). FE-SEM micrographs depict that the electrolyte layer is relatively dense, and porous fuel and air electrode layers are well adhered to the electrolyte. The i-V curves were obtained at a scan rate of 0.02 Vs⁻¹ from 0.3 to 1.5 V. Electrolysis current density increases as the temperature increases. SOEC performance increases, but SOFC performance decreases with increased water vapor concentration. Electrolysis current densities decrease as the CO₂ concentration increases. The i-V characteristics show only ohmic polarization under fuel-lean and fuel-rich conditions. At optimal conditions, current density values at 800 °C/1.5 V are -174, -187, and -195 mA cm⁻² for 5 %H₂O, 30 %CO₂, and 30 %CO₂/5 %H₂O co-electrolysis. At 800 °C, open-circuit voltage (OCV) values for H₂O, CO₂, and co-electrolysis are 0.906, 0.891, and 0.885 V, respectively. The electrolysis area-specific resistances (ASRs) give information on the reduction of CO₂ or H₂O, forming CO or H₂, respectively. At optimal conditions, ASR values are 3.43, 3.29, and 3.18 Ω cm² for H₂O, CO₂, and co-electrolysis, respectively. Co-electrolysis has a lower ASR value than pure H₂O and CO₂ electrolysis, indicating that H₂O and CO₂ are involved in the electrochemical processes.