Influence of CO₃²⁻ and C₂²⁻ on the Oxygen Evolution Performance of Perovskite La_0.7Sr_0.3FeO_3−δ Anode in Molten NaCl–CaCl₂

抄録

Electrochemical conversion of CO₂ into calcium carbide in molten salts has emerged as a promising route for carbon capture and utilization, enabling the production of acetylene, an important industrial chemical. However, continuous operation requires a stable oxygen evolution reaction (OER) at the anode while suppressing competing oxidation of carbonate and carbide species that regenerate CO₂. The anodic reaction mechanism in carbide-containing molten salts remains poorly understood. Here, the anodic behavior and durability of the perovskite oxide La_0.7Sr_0.3FeO_3−δ are investigated in molten NaCl–CaCl₂ at 873 K under controlled anionic environments containing O²⁻, CO₃²⁻, and C₂²⁻. Thermodynamic analysis using potential–pO²⁻ diagrams predicts that carbide oxidation occurs at the most negative potential, followed by carbon, oxide, and carbonate oxidation, which agrees with electrochemical measurements and gas analysis. When O²⁻ and CO₃²⁻ coexist, selective oxygen evolution is achieved with a Faradaic efficiency of 81.4 % and a low corrosion rate of 1.94 × 10⁻⁵ g cm⁻² h⁻¹. In contrast, dissolved C₂²⁻ undergoes anodic oxidation at lower potentials, producing amorphous carbon that accelerates electrode degradation and reduces OER efficiency. These results demonstrate that anodic stability is governed by the local anionic environment, highlighting the importance of maintaining O²⁻ and CO₃²⁻ coexistence while suppressing carbide transport to the anode.