Overpotential on Oxygen Evolving Platinu

To eliminate chloride gas emissions from aluminum electrolysis, this study investigates modifying a cryolite-based electrolyte by partially replacing sodium with potassium, which reduces the liquidus and allows operation at a temperature of 800°C. The research focuses on evaluating anodic polarization curves for platinum-based and Ni-Fe-Cu-based alloy compositions in a KF-NaF-AlF3-Al2O3(sat.) electrolyte, emphasizing the need for higher energy efficiency due to the increased anode potential. Results reveal that the polarization curve of the platinum anode displays two linear Tafel regions, while Ni-Fe-Cu anodes feature a single Tafel region. Notably, Ni-Fe-Cu anodes subjected to high-temperature air oxidation exhibit superior electrocatalytic activity compared to untreated counterparts. The study derives kinetic equations from a theoretical model to simulate overpotential and current, accounting for surface coverage. This model successfully predicts the experimentally observed Tafel regions on the platinum anode, suggesting a two-step charge transfer-controlled mechanism. The findings illustrate the correlation between multiple Tafel slopes and specific rate-determining steps, highlighting the potential for enhanced efficiency in aluminum electrolysis processes.