Newly Found Electrochemical Oscillations during Reduction of Nitrate Ions

Abstract

The electrochemical reduction of nitrate ions on Cu in strong acid solutions have been found to give two types of new oscillations both under potential controlled conditions and under current controlled conditions. The new oscillations occur during the reduction in HNO3 solutions and in H2SO4 solutions with KNO3. One of the new oscillations can be classified into a HNDR oscillator by electrochemical impedance measurements. Based on the experimental result that a little amount of hydrogen bubbles evolves due to the H+ reduction during the oscillation, we think that the NDR-hiding factor was the reduction current due to the reduction of hydrogen ions. The other new oscillation appears when hydrogen bubbles evolve intensely due to the reduction of water. The mechanism for the appearance of the oscillation awaits further investigation.