Interfacial properties and gas bubble formation during the electrolytic preparation of fluorine

During the electrolysis of fused KF-2HF strongly adherent bubbles of fluorine gas appear at the surface of the carbon anode. It was observed that the current is passing even when the anode was fully covered with a gas film. Impedance measurements performed in KF-2HF coupled with visual observations with a see-through cell show the existence of a conducting layer beneath the gas film. Experiments were performed to study the bubble growth by transient techniques. The results were interpreted in the frame of a model which shows the predominant role of the interfacial properties. A new approach, introducing capillary forces, leads to the concept of a variable curvature radius at the gas-liquid interface which is in agreement with the observed bubble shape. Digital simulation is used to describe the bubble growth and to calculate the values of interfacial parameters. (C) 2004 The Electrochemical Society.