Electrochemistry of nitrogen and nitrides in molten salts

Electrochemical behavior of nitrogen and nitrides in a molten LiCl-KCl-Li3N system has been investigated from thermodynamic and kinetic point of view. Nitride ions are anodically oxidized to form nitrogen gas almost quantitatively on a nickel electrode according to the following reaction:N3-=12N2+3e-.This is a reversible one-step three-electron reaction governed by a simple diffusion-controlled charge transfer process. The diffusion coefficient of nitride ion is estimated to be about 1.8 × 10−5 cm2 s−1 at 723 K. On the other hand, nitrogen gas is cathodically reduced almost quantitatively to form nitride ions, the reaction of which is expressed as12N2+3e-=N3-.The standard electrode potential of an N2/N3− couple, EN2/N3-0, at 723 K was found to be 0.382 V vs. Li+/Li. Potential-pN3− diagrams were constructed using EN2/N3-0 together with thermochemical data for elements relevant to the electrochemical reprocessing of nitride fuels. The obtained results also enable us to propose new processes such as the electrochemical formation of functional nitride films and the electrochemical synthesis of ammonia gas under ambient pressure.