Uncovering performance-enhancing strategy in plasma-based NH₃ cracking via chemical kinetics modeling

This study investigates the key performance characteristics of plasma-based NH₃ cracking, with a particular focus on warm plasmas, using a detailed plasma chemical kinetics model across a wide range of gas temperatures (T_g = 1000–6000 K) and mean electron temperatures (T_e = 0–3.5 eV). NH₃ conversion increases linearly with both T_g and T_e; however, the slope as a function of T_g drops when reaching full conversion. Full conversion is reached at 2300 K for pure thermal conversion, and already at 1100 K when electron impact (plasma) reactions are important under high T_e above 2.7 eV. The minimum energy cost for NH₃ conversion is calculated as 238 kJ/mol NH₃, when thermal dissociation is the driving cracking process. Importantly, in the T_g range of 1000–2700 K, the time required for complete NH₃ conversion is drastically reduced with increasing T_e—from thousands of years under purely thermal conditions to milliseconds with plasma assistance—primarily due to electron impact dissociation of NH₃. These differences between plasma-assisted and pure thermal cracking diminish at higher T_g and become absent when T_g > 2700 K. Two thermal reaction routes involving NH_x and N_xH_y fully dominate the entire cracking process. The product composition follows thermal equilibrium, and thus, it shifts as a function of T_g, with negligible influence of T_e. Our model demonstrates that plasma-based cracking enables rapid NH₃ conversion with reasonable energy cost, when T_g is around 2600 K, offering valuable insights for the development of energy-efficient NH₃ cracking plasma reactors for green H₂ production.