Origin of the Anodic Overvoltage Observed during Fluorine Evolution in KF ­ 2 HF

Abstract

The kinetics of the fluorine evolution reaction was studied in molten KF-2HF with a horizontal disk electrode in a large potential window. A new model was proposed recently for representing the electrode/electrolyte interface; it includes the presence of a “fluidized” layer between the surface carbon-fluorine film (C-F) generated on the carbon anode during electrolysis and the fluorine gas film. This model was confirmed here to be consistent. The fluidized layer is composed of liquid KF-2HF melt and dissolved fluorine gas. With our electrode geometry, it was shown that the main electroactive surface area is located at the lateral side of the disk electrode. Finally, the contributions of the C-F film, and of the fluidized layer, to the total anodic overvoltage, were studied using a numerical calculation method. It was shown that both contributions must be taken into account for a global understanding of the fluorine evolution process. © 2002 The Electrochemical Society. All rights reserved.