EFFECT OF CHEMICAL FLUORINATION OF CARBON ANODES ON THEIR ELECTROCHEMICAL PROPERTIES IN KF-2HF

Two kinds of carbon-fluorine surface layers on carbon electrodes were prepared and the electrochemical properties of these electrodes were s tudied in the KF-2HF melt. The first film was prepared in situ by elec trochemical oxidation of carbon in KF-2HF during the fluorine evolutio n reaction. The surface layer is mainly composed of conducting graphit e intercalation compounds, C-x,(HF)(y)F, usually denoted C-x,F. The se cond film was prepared ex situ by chemical fluorination of carbon with fluorine gas at 275 degrees C, leading to a mixture of C-x,F and grap hite fluorides, CFx. The fluorine evolution reaction is thus completel y inhibited in KF-2HF. XPS investigations have shown that ionic and co valent carbon-fluorine bonds are present in the C-x,F and CFx compound s, respectively. When doping aluminum particles were inserted into car bon before chemical fluorination, the fluorine evolution reaction occu rred due to the presence of C-x,F-AlF3 phases randomly scattered on th e electrode surface and within the film. It is supposed that the elect ron transfer occurs either directly from the electrolyte to the substr ate or by tunnel effect via intermediate-states, These particles also facilitate fluorine bubble detachment from the surface of the electrod e.