Electrocatalytic reduction of nitrite on a polycrystalline rhodium electrode

This paper addresses the mechanism of the electrochemical reduction of HNO2 and image on polycrystalline rhodium. Intermediates and/or reaction products were detected by means of various (combined) techniques: rotating ring-disk voltammetry (for NH2OH detection), online electrochemical mass spectrometry (for volatile products) and transfer experiments (for NOads). In acidic media, HNO2 depletion due to homogeneous-phase reactions generates dissolved NO: the latter species can be adsorbed at Rh and is reduced to N2O when 0.3 < E < 0.5 V (vs. RHE), while HNO2 is reduced in a diffusion-limited wave to mainly NH3 at potentials preceding hydrogen evolution. In alkaline media, the predominant product for the reduction of image when E < 0.2 V is still NH3, which can poison the electrode via dehydrogenation to NHx,ads species. For more positive potentials, reduction still occurs via NOads and stops at NH2OH 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, HNO2 and image is discussed.