Fluorine evolution reaction in KF-2HF: Influence of Ni-doping particles on the electrochemical properties of the carbon-fluorine surface film

Abstract

The influence of Ni-doped carbon electrodes on the electrochemical fluorine evolution process has been investigated using several kinds of carbon electrodes such as Ni-doped carbon electrodes, chemically fluorinated carbon, chemically fluorinated Ni-doped carbon. The chemical fluorination of carbon anodes was performed by fluorine gas at 275 °C. XPS investigations performed with respect to such kinds of samples have pointed out the presence of both ionic and slightly covalent carbon-fluorine bonds. Thus, this preparation mode leads to the formation of a mixed compound composed of graphite fluorides (CF x ) and G.I.C. (C x1 F). In the chemically fluorinated compound, the proportion of CF x with covalent C-F bonds is more important. For this reason, the fluorine evolution reaction in KF-2HF is strongly inhibited. Nevertheless, when doping nickel particles are inserted into carbon lattice prior to the chemical fluorination, the fluorine evolution reaction in KF-2HF occurred. The presence of nickel particles catalyse the formation of conducting C x1 F with ionic and/ or semi-ionic C-F bonds. In addition, the nickel particles are fluorinated during the fluorination process. The C x F-NiF y mixed compound is randomly scattered on the electrode surface and within the film and would enhance both the electron transfer at the carbon electrode and the fluorine bubbles detachment from the surface of the electrode.