Electrocatalytic ammonia oxidation over a nickel foam electrode: Role of Ni(OH)_2(s)-NiOOH_(s) nanocatalysts

Direct electrocatalytic oxidation of ammonia was carried out using an open-pore structured nickel foam electrode via electrochemical formation of Ni(OH)₂/NiOOH nano-flowers (theophrastite phase) on the nickel substrate at specific overpotentials. The electrode surface was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectrometer (RS), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammograms gave information on the nature of electron transfer between nitrogen species and nickel foam electrode and revealed the potential dependence nature of ammonia oxidation over the potential window of +0.7 V to +0.85 V (vs. Hg/HgO). Batch controlled potential experiments using nickel foam as the working anode in a three-electrode system were conducted to study the oxidation of ammonia in solution containing 0.1 M of Na₂SO₄ electrolyte, at pH 11 and temperature of 25 °C. Based on the current efficiency and reaction kinetics, it was possible to establish the mechanism of selective ammonia conversion to gaseous nitrogen and nitrate.