Online Electrochemical Detection of O^2- in Molten Carbonates

The behavior of oxide ions (O^2-) plays a critical role in electrochemical reactions in high-temperature molten salts. Nevertheless, a comprehensive understanding of O^2- behavior has been impeded by the lack of analytical methods. Herein, we developed an electrochemical system based on a YSZ-Pt oxide ion-sensing electrode for the online monitoring of O^2- activity in high-temperature molten salts. The YSZ-Pt electrode demonstrated a high degree of linearity (R² > 0.9998) in response to changes in O^2- activity in steady-state (nonelectrolytic) molten carbonates. Furthermore, the YSZ-Pt sensing electrode successfully revealed distinct differences in O^2- activity near the cathode and anode under dynamic (electrolytic) processes. In a molten salt CO₂ reduction reaction, the application of the O^2- sensor has, for the first time, provided direct evidence online of increasing O^2- activity near the cathode and decreasing O^2- activity near the anode. This work not only confirms the feasibility of in situ and online monitoring of O^2- during electrolysis but also establishes a promising methodology for investigating various high-temperature deoxygenation processes, such as aluminum electrolysis and nuclear fuel recycling.