Electrocatalytic reduction of nitrate in denitrification wastewater to ammonia: Electrode–electrolyte coupling to enhance the directed conversion performance

Wet absorption followed by electrocatalytic reduction is a promising two-step strategy for converting flue gas nitrogen oxides (NO x ) to resource ammonia (NH 3 ), and the electrode coupled with electrolyte can efficiently enhance the performance of nitrate (NO x − ) directed conversion to NH 3 . • Wet absorption coupled with electrocatalytic reduction converts flue gas NO x into NH 3 . • A high-performance electrode of Ni 2 P with strong electronic interactions was facilely prepared. • A NH 3 yield rate of 1068 ug·h -1 ·cm -2 with Faradaic efficiency of 85 % at - 0.58 V RHE was delivered. • The Ni 2 P electrode was well adapted to complex environments with stable performance. Wet absorption followed by electrocatalytic reduction is a promising two-step strategy for converting flue gas nitrogen oxides (NO x ) to resource ammonia (NH 3 ). The results showed that wet flue gas denitrification modeled with Na 2 SO 3 as the absorber could produce NO x − -N (NO 2 − -N and NO 3 − -N) at a concentration of 400 mg·L −1 , which was considered an excellent reactant for subsequent electrocatalytic reduction to produce NH 3 . Nickel phosphide (Ni 2 P) electrode with a three-dimensional network structure was prepared by a pure water hydrothermal-enhanced phosphatization strategy, and achieved a NH 3 yield rate of 1068 µg·h −1 ·cm −2 with Faradaic efficiency of 85 % in the electrocatalytic reduction of NO x − at − 0.58 V RHE . The Ni 2 P component with strong electronic interactions, was shown to be the real active site for the electrocatalytic NO x − reduction, where the conversion of NO 3 − to NO 3 * was the rate-limiting step for NH 3 production. Furthermore, the results of tert -butanol quenching and electron paramagnetic resonance demonstrated that the indirect pathway of atomic hydrogen (H*) mediated NO x − reduction dominated in the Ni 2 P electrode. In addition, the working potentials and electrolyte characteristics (including NO x − concentration, electrolyte concentration and pH) affected the performance of NH 3 production, whereas the Ni 2 P electrode was well adapted to complex environments with stable performance. This study presented a novel strategy for the treatment of denitrification wastewater using cost-effective Ni 2 P electrode.