Microscopic-Level Insights into the Mechanism of Enhanced NH 3 Synthesis in Plasma-Enabled Cascade N 2 Oxidation-Electroreduction System.

Integrated/cascade plasma-enabled N 2 oxidation and electrocatalytic NO x - (where x = 2, 3) reduction reaction (pNOR-eNO x - RR) holds great promise for the renewable synthesis of ammonia (NH 3 ). However, the corresponding activated effects and process of plasma toward N 2 and O 2 molecules and the mechanism of eNO x - RR to NH 3 are unclear and need to be further uncovered, which largely limits the large-scale deployment of this process integration technology. Herein, we systematically investigate the plasma-enabled activation and recombination processes of N 2 and O 2 molecules, and more meaningfully, the mechanism of eNO x - RR at a microscopic level is also decoupled using copper (Cu) nanoparticles as a representative electrocatalyst. The concentration of produced NO x in the pNOR system is confirmed as a function of the length for spark discharge as well as the volumetric ratio for N 2 and O 2 feeding gas. The successive protonation process of NO x - and the key N-containing intermediates (e.g., -NH 2 ) of eNO x - RR are detected with in situ infrared spectroscopy. Besides, in situ Raman spectroscopy further reveals the dynamic reconstruction process of Cu nanoparticles during the eNO x - RR process. The Cu nanoparticle-driven pNOR-eNO x - RR system can finally achieve a high NH 3 yield rate of ∼40 nmol s -1 cm -2 and Faradaic efficiency of nearly 90%, overperforming the benchmarks reported in the literature. It is anticipated that this work will stimulate the practical development of the pNOR-eNO x - RR system for the green electrosynthesis of NH 3 directly from air and water under ambient conditions.