New insights into the mechanism of nitrite reduction on a platinum electrode

Abstract

This paper reinvestigates the mechanism of HNO 2 and NO 2 - reduction on polycrystalline platinum as a function of electrolyte pH and reactant concentration. Intermediates and/or reaction products were detected by means of various (combined) techniques: RRDE (for NH 2OH detection), OLEMS (for volatile products) and FTIRS. In acidic media, HNO 2 is depleted due to homogeneous-phase reactions (accelerated by stirring) that generate NO: the latter species, which readily forms an adlayer on Pt, is reduced in a first wave to N 2O, while HNO 2 is reduced in a following diffusion-limited wave to mainly NH 2OH. The two waves display different reaction orders. Loss of HNO 2 (as NO) in the blanketing Ar stream hampered an accurate quantitative evaluation of the product distribution. When the pH is increased, NO 2 - is reduced in a single peak with a much lower current density than in the previous case. In RDE experiments, the peak was found to decrease with increasing rotation rates. The presence of a sluggishly reduced intermediate (NH 2OH) has been proposed. A general mechanistic scheme, including NO, HNO 2 and NO 2 - , is discussed.