Understanding Anode Overpotential

In aluminium electrolysis cells the anodic process is associated with a substantial overpotential. Industrial carbon anodes are produced from coke materials, but the effect of coke type on anodic overpotential has not been well studied. In this work, labscale anodes were fabricated from single source cokes and electrochemical methods were used to determine the overpotential of the anode materials. Attempts were then made to explain these trends in terms of both the physical and chemical characteristics of the baked anodes themselves and their raw materials. Routine coke and anode characterisation methods were used to measure properties such as impurity concentrations and reactivity (to air and CO₂), while non-routine characterisation methods were applied to study surface and structural properties. It was found that the overpotential trend of the anodes correlated well with many of the properties studied, and explanations for these observed correlations are suggested. These findings offer exciting possibilities for reducing the energy demand of the anodic process.