ON THE ELECTROCHEMICAL REDUCTION OF NITRATE ION IN THE PRESENCE OF VARIOUS METAL IONS

The role of electrode-inert metal ions (Zr(IV), Hf(IV), La(III), Mg(II), Ca(II), Sr(II), Ba(II) and Li(I)) in electrochemical reduction of nitrate ion is discussed on the basis of polarographic measurement. No evidence for nitrate-metal ion complexes in the bulk solution was found from UV and Raman spectra under our experimental conditions. No large differential capacity (no double-layer effect) which might be assigned to strong adsorption was observed for all the metal ion solutions. However, our results indicated that the metal ion acted as an intermediary for the charge transfer from the electrode to the nitrate ion and as a proton supplier to the nitrate by the hydrolysis of the metal ion itself in the proximity of the electrode.