Experimental investigation of discharge characteristics in AC-driven rotating arc plasma for ammonia decomposition

This study investigates an AC-driven rotating arc plasma reactor for ammonia decomposition using pure NH₃ at 10 NLPM. Nitrogen and N₂/H₂ (1:3 vol%) mixtures were employed as reference gases to elucidate the intrinsic discharge behavior of ammonia, while the effect of reactor geometry was examined by introducing a converging nozzle. Stable discharges were achieved at ∼20 kHz and 0.75–1.6 A. Ammonia discharge exhibited distinct hysteretic V I behavior and higher re-ignition voltages due to reduced discharge memory, accompanied by an ammonia-derived orange emission region. Unlike previous studies that mainly emphasized overall conversion performance, the present work focuses on the NH₃-specific discharge physics of an AC-driven rotating arc and its linkage to reactor performance. NH₃ conversion increased with power, reaching 41.7% at 1.21 kW, yielding 6.3 NLPM H₂ with an SEI of 174.4 kJ/mol_NH 3 (7.3 kJ/L), corresponding to an H₂ energy yield of 310.2 L/kWh. A converging nozzle reduced gas residence time by ∼17%, resulting in up to 9% lower conversion. The results indicate that maintaining a sufficiently high arc voltage and preserving gas–arc interaction time are more critical for efficient NH₃ decomposition than simply increasing the applied current. • Unique orange luminescence indicates thermal NH₃ decomposition around arc column. • First comprehensive V I characteristics of AC-driven NH₃ rotating arc plasma. • Ammonia discharge shows larger voltage hysteresis than N₂ due to H₂ diffusion. • Extended arc length and residence time critical for maximizing decomposition. • Results reveal critical design guidelines for plasma-assisted NH₃ cracking reactors.