Solid oxide electrolysis cells (SOECs) for converting CO₂ to more useful chemical species are attracting considerable attention because of their high electrolytic efficiency, offering the possibility of direct conversion of CO₂ to CO (CO₂ → CO + 1/2O₂). In addition, recently, high temperature electrolysis of steam to H2 is also attracing much interest. Heat energy supplied to SOECs can maximize electrolysis efficiency, offering both thermodynamic and kinetic advantages. The generated CO can be used as a fuel gas, converted into syngas via reaction with H₂, or to reduce iron oxide to pure iron in the iron-making process. The application of SOECs and related technologies can contribute to a more sustainable economy. For the electrolyte in SOECs, ZrO₂ doped with 8 mol% of Y₂O₃ (YSZ) has always been used because of its chemical stability and mechanical strength. However, an electrolyte for CO₂ or H2O electrolysis with lower internal resistance and increased efficiency is highly desirable. LaGaO₃-based electrolytes have higher oxide-ion conductivities and transport numbers, which can lead to higher energy conversion efficiency; hence, a doped-LaGaO₃ electrolyte (La_0.9Sr_0.1Ga_0.8Mg_0.2O₃, LSGM) has been tested in this study. For CO₂ and H₂O electrolysis, another drawbacks is durability since electrode is easily aggregated and deactivated.

Although metals, particularly Ni, are widely used as cathodes in CO₂ electrolysis cells, we found that a LaFeO_3−δ-based perovskite cathode (La_0.6Sr_0.4Fe_0.8Mn_0.2O_3−δ, LSFM6482) showed the highest activity for CO₂ and H₂O electrolysis among the examined oxides Among the cells using a La_0.6Sr_0.4Fe_0.9M_0.1O_3−δ-based oxide cathode (M = Mn, Co, Ni, or Cu) for CO₂ electrolysis at 1073K. Mn was the most effective Fe replacement on the B site, and the La_0.6Sr_0.4Fe_0.9Mn_0.1O_3−δ cathode showed the highest activity and current density for CO₂ electrolysis of this set of cathodes. Among the tested dopants, Mn and Co have ionic sizes most similar to Fe and a smaller size mismatch between the host and dopant cations in the perovskite structure, which should suppress dopant segregation and minimize detrimental effects of cation segregation. Overall, among the examined cations, Mn was the best dopant for the B site of the LaFeO₃ cathode. A cell consisting of BLC64/LSGM/LSFM6482 exhibited the highest CO₂ electrolysis activity (a current density of 0.52 A/cm² at 1.6 V and 1173 K) of all cathodes investigated in this study and reduced CO₂ at a rate of 153 μmol/cm²•min at 1173 K and 1.6 V with negligible carbon formation. In this study, change in internal resistance during electrolysis is also discussed based on impedance measurement.