Performances of metal fluoride added carbon anodes with pre-electrolysis for electrolytic synthesis of NF 3

Abstract

Metal fluoride added carbon anodes treated by pre-electrolysis were investigated for electrolytic production of nitrogen trifluoride (NF 3) in molten NH 4F·KF·4HF at 100 °C. The conditions for pre-electrolysis were first optimized using a graphite sheet anode as a model anode. The formation of fluorine-graphite intercalation compounds (fluorine-GICs) with semi-covalent C–F bonds, (C x F) n , on the MgF 2 and CaF 2 added carbon anode surface was accelerated by pre-electrolysis at potentials less than 4.0 V. Critical current densities (CCD) on the MgF 2 added carbon anodes pre-electrolyzed under various conditions were determined, and the highest CCD was 290 mA cm −2 obtained for that pre-electrolyzed at 3.5 V for 500 C cm −2. This anode was successfully used in the electrolysis at 100 mA cm −2 for 290 h and the maximum NF 3 current efficiency was 55%. From these results, it was concluded that the metal fluoride added carbon anode treated by pre-electrolysis has a high potential for electrolytic production of NF 3 at higher current density.