Electrochemical reduction of NO by alternating current electrolysis using yttria-stabilized zirconia as the solid electrolyte: Part I. Characterizations of alternating current electrolysis of NO

The electrochemical promotion of the decomposition of NO in the presence of excess O2 was carried out by applying AC voltages lower than 6 V at frequencies from 0.01 to 103 Hz to a YSZ cell having two same-metal electrodes, Au, Pd, Pt or Rh. The Pd and Pt electrodes were relatively effective for this reaction. This could be explained by their electrochemical oxygen-pumping properties and catalytic activities for the reduction of NO. The promotional effect was the most enhanced at a frequency of 0.1 Hz and became larger as the concentration of NO increased or the concentration of O2 decreased. Most of the product was N2, although a small amount of N2O was observed at low conversion of NO. The comparison of AC electrolysis with DC electrolysis showed that the former had a somewhat lower current efficiency for the decomposition of NO than the latter at lower than 3 V, above which the opposite result was observed. In addition, DC electrolysis brought about a significant deterioration of the cell, but AC electrolysis did not result in such a deterioration even at a high voltage of 4 V.