Electrocatalytic reduction of nitrite on a polycrystalline rhodium electrode

摘要

This paper addresses the mechanism of the electrochemical reduction of HNO_2 and NO2- 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 NO2- 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 NO2- is discussed.