Anodic behaviors of nickel and platinum in a mixed molten salt of (CH3)(4)NF center dot 4HF and CsF center dot 2HF at room temperature

The electrical conductivity of mixed melts of Me4NF . 4HF (Me=CH3) and CsF . 2HF decreased with increasing the ratio of CsF . 2HF in the mixed melts, because of the increase of its viscosity. The anodic reaction on nickel in the mixed melt of Me4NF . 4HF and 50 wt% CsF . 2HF seemed to vary with incr easing potential, permitting division into four regions as follows: anodic dissolution of nickel in region I (ca, 0.2 V vs. Ag/AgClO4), passivation of the Ni anode in region II (ca. 0.5-4.0 V), oxidation of Ni(II) compounds s uch as NiO, NiF2, and/or oxyfluoride in the film formed on the Ni anode to Ni(III) and/or Ni(IV) compounds and electrochemical fluorination of Me4N+ i n region III (4.0 similar to 6.0 V), and also electrochemical fluorination of Me4N+ in region TV (higher than 6.0 V). The oxidized layer formed on the Ni anode in regions III and IV was composed of nickel difluoride (NiF2) wi th a small amount of nickel oxides having plural valencies, a highly oxidiz ed nickel fluoride and/or oxyfluoride. The amount of a highly oxidized nick el fluoride or oxyfluoride formed on the Ni anode was increased by addition of CsF . 2HF into the melt of Me4NF . 4HF. Anodic reaction on platinum was also investigated in the same mixed melt and electrochemical fluorination seemed to take place at potentials higher than 3.0 V. The XPS analysis reve aled that platinum oxide such as PtO and PtO2 remained on the Pt anode pola rized at 3.0 V and that the content of platinum fluoride in the oxidized la yer increased with the increase of potential. The corrosion of the Pt anode was stimulated at potentials higher than 3.5 V. (C) 1999 Elsevier Science S.A. All rights reserved.