Efficient and highly selective direct electrochemical oxidation of ammonia to dinitrogen facilitated by NiCu diatomic site catalysts

Direct electrochemical oxidation has recently received increasing attention in ammonia-nitrogen wastewater treatment. However, how to catalyze the oxidation of ammonia to N-2 with high selectivity retains a tremendous challenge. In this work, NiCu3-N-C diatomic site catalyst (DAC) anchored in nitrogen-doped carbon was synthesized via solid-phase pyrolysis. HAADF-STEM and XAFS characterizations demonstrated the high dispersion of adjacent Ni/Cu diatomic sites and the micro-environment of Ni-N-4/Cu-N-4 groups. The experiment results exhibit that NiCu3-N-C DAC has an eminent intrinsic activity towards AOR with a TOF of 3.64 s(-1) at 1.50 V vs. RHE. Consequently, in a real wastewater with 616 mg/L NH4+-N, 99.52% of removal efficiency and 86.60% of faradaic efficiency (FE) after a 6-hour degradation experiment were acquired with a high N-2 selectivity of 97.87%, confirming its excellent catalytic performance. This work furnishes a good example of rationally designing functionally coordinated diatomic site catalysts (DACs) for the efficient treatment of ammonia-nitrogen wastewater.