High yield ammonia production via glucose oxidation assisted electrochemical nitrate reduction

Abstract

Electrocatalytic nitrate (NO₃^-) reduction reaction (NO₃RR) provides a potential route for the synthesis of value-added ammonia (NH₃) and removal of nitrate pollutants. However, this reaction is limited by nitrate adsorption and slow kinetics involving multiple proton and electron transfer steps. The sluggish OER can hinder NO₃RR performance, but replacing it with a more facile oxidation process enhances performance. Herein, we have demonstrated glucose oxidation assisted NO₃RR, utilizing CuNi(1:2)S as a bifunctional catalyst demonstrating high NH₃ Faradaic efficiency (F.E.) of 93.44% with a yield rate of 4.7 mg h^-1 cm^-2 or 280.47 mmol gcat^-1 h^-1 at -0.4 V vs. RHE along with achieving high current densities applicable at industrial levels and its high activity compared to monometallic variants was explained using the ultraviolet photoelectron spectra (UPS) technique. Further, a mechanistic study using in-situ electrochemical Raman spectroscopy, illustrates the hydrogenation of NO₃^- to NH₃ via NO₂^- intermediate. Moreover, replacing OER with glucose oxidation reaction (GOR) in full cell system could decrease the total energy input by 200 mV and increase the NH₃ yield from 120.95 µg h^-1 cm^-2 to 259.46 µg h^-1 cm^-2. Furthermore, the high value-added products were obtained at both anode and cathode at a low cell voltage. More interestingly, we demonstrate the practical extraction of high-purity NH₄Cl (s) and NH₃ aqueous product from electro-reduced NO₃^- after electrolysis at 100 mA cm^-2 for 50 h, with a collection efficacy of 89.84% of condensed NH₃ (aq) solution.