Nitrous acid electroreduction on macroporous silver foam

Abstract

In this paper, silver 3D foams have been synthesized using dynamic hydrogen bubble template and thiocyanate-based deposition bath. The material was used as electrocatalyst for nitrous acid (HNO2) reduction. On this material, we found that overpotential of nitrous acid reduction is decreased by at least 300 mV and the in situ formed nitric oxide (NO) reduction becomes the predominant step when the potential is decreased even further, comparing to flat silver polycrystalline electrode. Another difference between this material and the silver polycrystalline electrode concerns the influence of the nature of supporting electrolyte on the preferred reaction. Precisely, while Ag polycrystalline is preferentially reducing HNO2 into NO in low concentration of perchlorate electrolyte, Ag foam preferentially reduces the in situ formed NO into N2O, in all tested electrolytes, if the same potential range is considered. The initial reduction of HNO2 into NO is better evidenced after the partial removal of thiocyanate species. Finally, the use of isotope 15N in the nitrite salt and of a flow thin layer cell enabled the detection of nitrogen among other gaseous products for both silver foam and flat silver electrode.