Effect of CsF-concentration on electrolytic conductivity, viscosity and anodic reaction of nickel electrode in (CH3)3N-CsF–HF system at room temperature

In order to increase the formation ratio of perfluorotrimethylamine, (CF3)3N, to overall anode gas in electrolytic production using Ni anode, mixed melts of (CH3)3N·mHF + CsF·2.3HF were used as electrolytes at room temperature. The ionic conductivity of the mixed melts decreased with an increase in the CsF concentration, whereas the viscosity of the mixed melts increased with increasing the CsF concentration. AC impedance and XRD analysis revealed that the presence of CsNi2F6 in the oxidized layer formed on the Ni anode after electrolysis. The gas evolved at the Ni anode was composed of (CF3)3N, (CF3)2CHF2N, CF3(CHF2)2N, (CHF2)3N, CF4, NF3, CHF3, C2HF5, and C2F6. The best ratio of (CF3)3N to the overall anode gas (52.11%) was obtained in the electrolyte of (CH3)3N·5.0HF + 50 wt% CsF·2.3HF mixed melt at 20 mA cm−2.

Research highlights
► We improved an electrolytic production method of perfluorotrimethylamine, (CF3)3N, on Ni anode by using a mixed melt system of (CH3)3N×5.0HF + x wt% CsF×2.3HF as electrolyte at room temperature.
► Charge transfer resistance during the electrolysis was reduced by addition of CsF×2.3HF because CsNi2F6 with a high electronic conductivity was present in the oxidized layer formed on Ni anode after electrolysis.
► The best ratio of (CF3)3N to the overall anode gas (52.11%) was obtained in the electrolysis of (CH3)3N×5.0HF + 50 wt% CsF×2.3HF at 20 mAcm-2.