Investigating the kinetics and reaction pathways for water and carbon dioxide co-electrolysis in Molten carbonate cells

Molten Carbonate Electrolysis Cells (MCECs) represent a promising technology for hydrogen production and carbon dioxide utilization. Despite extensive studies on Molten Carbonate Fuel Cells (MCFCs), the electrode kinetics in MCECs remain less explored, particularly for hydrogen evolution. This work investigates the reaction orders of H 2 O and CO 2 in the electrolysis reaction by estimating the exchange current densities through the Butler-Volmer equation. The analysis is conducted on polarization curves obtained experimentally on a lab-scale molten carbonate cell. Results show that CO 2 and H 2 O play a similarly significant role in determining the reaction rate, as indicated by their comparable reaction orders. This suggests that the rate-determining step (RDS) is partially influenced by mass transport limitations. Additionally, reaction orders remain consistent across different temperatures, indicating that the nature of the RDS does not change within the range investigated. The standard exchange current density increases with temperature, suggesting the presence of kinetic limitations and supporting the hypothesis that the RDS is under mixed kinetic-diffusion control.