Electroactivity of hydrogen–nitrogen compounds in ionic liquids. Platinum rotating-disc electrode voltammetric behaviour of ammonia in the (Na, K)NO3 equimolar melt

Abstract

In the context of a systematic investigation on light-fuel electrodes in ionic solvents, the voltammetric behaviour of ammonia was studied in the (Na, K)NO₃ equimolar melt at 518 K.

Solutions containing NH₃, NH₃+ H₂O, NH₃+ NO^–₂ were tested by using platinum rotating-disc electrode systems. Mechanistic models for the electro-oxidation and electroreduction reactions of ammonia are suggested which fit the experimental electrochemical findings and, in particular, the constant value of the ratio between the electroreduction and the electro-oxidation limiting currents of ammonia. The diffusion coefficient of ammonia in the given experimental conditions was estimated to be 1.9 × 10^–5 cm² s^–1 at the given temperature.

The chemical behaviour of amide ions, which are involved in the ammonia electroreduction pathway, is described.

‘Concealed limiting-current’ phenomena observed when ammonia is flowed in nitrite-containing melts are explained on the basis of acid–base reactions between each of these two species and the electro-oxidation product of the other.