Influences of graphite anode area on electrolysis of solid metal oxides in molten salts

Chen, Hualin; Jin, Xianbo; Yu, Linpo; Chen, George Z.

Abstract

Laboratory studies of electrochemical reduction of refractory metal oxides, e.g. TiO2 and Ta2O5, in molten CaCl2 often involve a graphite anode and a cell voltage of 3.0 V or higher, which deviates significantly from thermodynamic predictions. The causes considered in the past have included mechanistic, kinetic and dynamic complications of cathode reactions, but little was considered on anodic processes. This paper shows that oxidation of the O2− ion on the graphite anode is also a significant contributor to the high cell voltages applied. Cyclic voltammetry in molten CaCl2 containing added CaO (up to 2.51 mol%) suggested that O2− oxidation on graphite proceeds dominantly in two steps as previously observed on glassy carbon. With increasing CaO concentration, the second step became rate-limiting over a wide range of potentials before the processes reached at diffusion controlled high current density. This understanding led to the proposal and experimental confirmation of a “low anode current density strategy” in potentiostatic reduction of thin cylindrical pellets of TiO2 and Ta2O5 in molten CaCl2 at 850 °C. It was observed that a 10-fold increase of the graphite anode area could decrease the cell voltage by about 1.0 V, which should save energy consumption by up to one third.

Citation

Chen, H., Jin, X., Yu, L., & Chen, G. Z. (2014). Influences of graphite anode area on electrolysis of solid metal oxides in molten salts. Journal of Solid State Electrochemistry, 18(12), 3317-3325. https://doi.org/10.1007/s10008-014-2645-2

• Journal Article Type: Article
• Online Publication Date: Oct 11, 2014
• Publication Date: 2014-12
• Deposit Date: Aug 4, 2024
• Publicly Available Date: Oct 24, 2024
• Journal: Journal of Solid State Electrochemistry
• Print ISSN: 1432-8488
• Electronic ISSN: 1433-0768
• Publisher: Springer Verlag
• Peer Reviewed: Peer Reviewed
• Volume: 18
• Issue: 12
• Pages: 3317-3325
• DOI: https://doi.org/10.1007/s10008-014-2645-2
• Keywords: Graphite anode . Oxide ion oxidation . Metal oxides . Electrolysis .Moltencalciumchloride .Energysaving
• Public URL: https://nottingham-repository.worktribe.com/output/3213725
• Publisher URL: https://link.springer.com/article/10.1007/s10008-014-2645-2