Unraveling the Defluorination Mechanism of Sodium Fluoro-Aluminates on Graphite: A First-Principles Study

The graphitized carbon blocks are used as cathode and anode materials on modern aluminum electrolyzers, which provide a reaction interface between molten salts and a graphitized cathode for the electrochemical reaction. The first-principle calculations were performed to clarify the defluorination mechanism of fluoro-aluminates on graphite cathodes in aluminum electrolysis for energy efficiency and carbon emission reduction. The adsorption behaviors of intermediates involved in defluorination reactions on graphite surfaces are analyzed, revealing their spontaneous adsorption based on their adsorption energies and charge density differences. Furthermore, the defluorination pathways of both single Na₃AlF₆ clusters and fluoride-aluminate polymers are elucidated. Notably, Na₃AlF₆, after undergoing the thermochemical defluorination process to obtain AlF₃, preferentially undergoes electrochemical defluorination via Al-F-Al polymerization. The key findings indicate that the chemical defluorination of Na₃AlF₆ leading to NaAlF₄ serves as a pivotal step, facilitating the overall defluorination process and enhancing the aluminum production efficiency. This work provides fundamental insights into optimizing aluminum electrolysis processes.