The development of cathode materials with high catalytic activity and low cost is a challenge for CO2 electrolysis based on solid oxide electrolysis cells. Herein, we report a low-cost and highly active metallic Fe nanoparticle-decorated Ruddlesden-Popper (La, Sr)­FeO4+δ cathode catalyst (Fe-RPLSF), which shows a high oxygen vacancy concentration and robust CO2 reduction rate. At 850 °C, the current density of the electrolysis cell with the Fe-RPLSF cathode reaches −1920 mA cm–2 at a voltage of 1.5 V, and the Faraday efficiency is as high as 100%. The polarization resistance at low frequency (0.1–10 Hz), which is the rate-limit step for CO2 electrolysis, significantly decreases with the exsolved Fe nanoparticles because of improved CO2 dissociative adsorption. Moreover, our electrolysis cell demonstrates acceptable short-term stability for direct CO2 electrolysis.

Solid oxide cells (SOCs) can switch between fuel cell and electrolysis cell modes, which alleviate environmental and energy problems. In this study, the La0.3Sr0.7Fe0.9Ti0.1O3−δ (LSFTi 91) perovskite is innovatively used as a symmetric electrode for solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs). LSFTi 91 exhibits a pure perovskite phase in both oxidizing and reducing atmospheres, and the maximum conductivity in air and 5% H2/Ar is 150 and 1.1 S cm–1, respectively, which meets the requirement of the symmetric electrode. The polarization resistance (R p) at 1.5 V is as low as 0.09 Ω cm2 in the SOEC mode due to the excellent CO2 adsorption capacity. The current density can reach 1.9 A cm–2 at 1.5 V and 800 °C, which is the highest electrolytic performance in the reported single-phase electrodes. LSFTi 91 also exhibits eminent oxygen reduction reaction and hydrogen oxidation reaction (ORR and HOR) activities, with R p of 0.022 and 0.15 Ω cm2 in air and wet H2, respectively. The peak power density of SOFC could reach 847 mW cm–2 at 800 °C. In addition, good reversibility is confirmed in the cyclic operation of SOFC and SOEC.

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Co-free La 0.5 Sr 0.5 Fe 0.9 Nb 0.1 O 3-δ (LSFNb) perovskite oxide is synthesized by the sol-gel method. LSFNb oxide exhibits good chemical and structural stability in both oxidizing and reducing atmospheres. Therefore, symmetric cells with the configuration LSFNb/LSGM/LSFNb are prepared and the electrochemical performance is evaluated for both solid oxide fuel cell (SOFC) and solid oxide electrolysis (SOEC) applications. The LSFNb symmetric electrode presents excellent catalytic activity in both SOFC and SOEC modes. At 850 • C, the peak power density of the symmetric cell reaches 1157 mW cm −2 in SOFC mode, while the current density exceeds 1460 mA cm −2 at 1.3 V in SOEC mode. Under H 2 O/CO 2 co-electrolysis at 800 • C, the H 2 and CO production rates reach 2.19 and 2.77 mL min −1 cm −2 at −708 mA cm −2 with nearly 100% faradaic efficiency. Moreover, the symmetric cell displays good stability under CO 2 and H 2 O co-electrolysis, indicating that LSFNb oxide is a promising symmetric electrode material for steam and CO 2 co-electrolysis as well as for regenerative fuel cells.