Catalyst-free ammonia decomposition under atmospheric pressure and nanosecond-pulsed DBD: energy deposition dynamics and its role in hydrogen production

Abstract

Non-thermal plasma technology provides a promising route for ammonia decomposition to hydrogen under atmospheric pressure and relatively mild thermal conditions. In this study, ammonia decomposition was investigated in a coaxial dielectric barrier discharge reactor driven by alternating current (AC) and nanosecond pulse (NP) excitation. The effects of waveform parameters, including pulse width, rise time, and fall time, on the electrical characteristics and ammonia decomposition performance were systematically examined. In addition to NH₃ conversion and H₂ yield, an energy utilization efficiency (EUE) metric was introduced as a comparative indicator to evaluate the effective use of input energy under different operating conditions. The results show that the NP-DBD system outperforms the AC-DBD system, achieving up to 99.5% NH₃ conversion under nanosecond pulse excitation conditions associated with enhanced transient excitation. Increasing the pulse width prolongs the temporal energy deposition process and improves the effective use of deposited energy, leading to higher NH₃ conversion and improved EUE performance. Rise time also affects the reaction behavior, whereas the influence of fall time is comparatively weaker. Gas temperature analysis gave a rotational temperature range of 388–597 K and a reaction-gas temperature range of 297–395 K, suggesting that high NH₃ conversion can be achieved with comparatively limited macroscopic gas heating under NP excitation. This study clarifies how pulse-parameter modulation influences energy deposition and ammonia decomposition behavior under atmospheric-pressure NP-DBD, and provides useful insight into catalyst-free NH₃-to-H₂ conversion under mild conditions.