Electrocatalytic reduction of nitrite on a polycrystalline rhodium electrode

Abstract

This paper addresses the mechanism of the electrochemical reduction of HNO 2 and NO 2 - on polycrystalline rhodium. Intermediates and/or reaction products were detected by means of various (combined) techniques: rotating ring-disk voltammetry (for NH 2OH detection), online electrochemical mass spectrometry (for volatile products) and transfer experiments (for NO ads). In acidic media, HNO 2 depletion due to homogeneous-phase reactions generates dissolved NO: the latter species can be adsorbed at Rh and is reduced to N 2O when 0.3 < E < 0.5 V (vs. RHE), while HNO 2 is reduced in a diffusion-limited wave to mainly NH 3 at potentials preceding hydrogen evolution. In alkaline media, the predominant product for the reduction of NO 2 - when E < 0.2 V is still NH 3, which can poison the electrode via dehydrogenation to NH x ,ads species. For more positive potentials, reduction still occurs via NO ads and stops at NH 2OH for E > 0.3 V. The behavior of Rh is compared to Pt and explained in terms of general properties of these metals. A mechanistic scheme including NO, HNO 2 and NO 2 - is discussed.