Effect of anode materials on NF3 formation

The electrolytic formation of NF3 from molten salt, NH4F-HF, KF-NH4F-HF, and CsF-NH4F-HF, with different anodes, was compared. The current efficiencies for NF3 formation on a Ni anode and a LIF impregnated carbon (LiF/C) anode in the NH,F-HF melt increased with an increase of the current density and became constant at current densities higher than 120 and 50 mA/cm(2), respectively. Current efficiencies on the Ni anode were greater than those on the LiF/C anode in the range of current density higher than 30 mA/cm(2). On the other hand, the presence of KF in the melt reduced the NF3 current efficiency on both the Ni and the LiF/C anodes, and the NF3 current efficiency on the LiF/C anode in the KF-NH4F-HF melt decreased with an increase of the current density. According to the surface analyses, the oxide film on the Ni anode polarized in the NH4-F-HF melt was composed of nickel difluoride, some highly oxidized nickel fluoride, and nickel oxide or oxyfluoride having plural valences. Consequently highly oxidized nickel fluoride on the Ni anode is considered to function as a mediator of the electrochemical fluorination under discussion.