Ammonia (NH3) discharged from wastewater is a major cause of eutrophication, raising concern for the pollution of the aquatic ecosystem. Direct electrochemical oxidation of ammonia (AEO) has been extensively applied using Pt and Pt-based electrodes due to their high activity towards NH3. However, Pt is expensive to commercialize, and it is susceptible to being poisoned by the N during AEO. Therefore, developing a low-cost electrode material featuring high electrocatalysts and low overpotential is highly urgent. This study fabricated a Cu/Nickel foam (NF) electrode by electrodeposition of Cu particles on NF substrate. The effect of initial pH (8-11) and applied voltage (0.7-1.1V vs Hg/HgO) on NH3 removal and N products selectivity (e.g. SN2, SNO2-, SNO3-) were systematically investigated for 5 h reaction. The electrochemical analysis showed that Cu/NF exhibited a two-time higher current density with a 4.7 time larger electrochemical surface area than those obtained by NF under the presence of NH3. X-ray photoelectron spectroscopy analysis confirmed that Cu(OH)2 and NiOOH catalysts were electrochemically formed during AEO reaction. The highest NH3 removal (60%) for Cu/NF was achieved at pH 11 at a voltage of 1.1 V, which was 21% higher than NF. In addition, the formation of toxic nitrite was inhibited using Cu/NF under the same applied voltage. Interestingly, the N products selectivity was of time-dependent. At pH 8, SNO3- decreased gradually with electrolysis time while SNO3- increased at pH 9-10. At pH 11, SNO3- barely changed during the 5 h reaction time. On the other hand, at applied voltage of 0.9 V, a sharp increase of SNO3- with the time proceeding was observed. At 1.0 V, the increase of SNO3- became more gradual during the AEO. This study provides insightful knowledge regarding the effect of operation conditions on NH3 removal as well as N products selectivity using Cu/NF electrode.

Enhanced electrochemical oxidation of ammonia on the Cu/Ni foam electrode: Effect of pH and applied voltage on N products selectivity

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