Hydroxylamine Oxidation Electrocatalysis on Carbon

Hydroxylamine (NH₂OH) is a major intermediate in the nitrogen cycle, and its electro-oxidation in alkaline media is key for using nitrogen-based fuels in alkaline fuel cells. Iron- and nitrogen-codoped carbons (FeNCs) are promising electrocatalysts, with Fe-N_x active sites resembling heme (FeN₄) centers in enzymes. We report an FeNC catalyst for the hydroxylamine oxidation reaction at E = 0.60 V vs RHE at pH 14. Using a range of control materials, we reveal that the iron plays no significant role in the reaction, whereas the carbon support (reduced graphene oxide) becomes catalytic after a cathodic activation scan. The two voltametric waves for hydroxylamine oxidation on carbon are diffusion-controlled, irreversible, independent of each other, and are more active than either edge or basal plane graphitic sites. Differential electrochemical mass spectroscopy and ion chromatography correlate the oxidation waves with the formation of N₂O and NO₂ (starting at early potentials) and nitrite and N₂ at higher potentials. The electrochemical reactions are coupled with chemical oxidation or disproportionation steps. The reaction mechanism proposed in this study for hydroxylamine oxidation on carbon provides valuable insights for the development of electrocatalysts for nitrogen-based fuels in alkaline devices.