Multi-Scale Modeling for Plasma-Enhanced Ammonia Decomposition over Carbides and Nitrides

Ammonia is a carbon-free hydrogen carrier, but its decomposition typically requires high temperatures over costly Ru-based catalysts due to the large barrier for NN bond formation. We develop a multiscale framework combining density functional theory, zero-dimensional plasma kinetics, and microkinetic modeling to elucidate how non-thermal plasma (NTP) enables low-temperature NH₃ decomposition over Co-based carbides and nitrides, benchmarked against Ru and Co. Under thermal conditions, all catalysts are limited by NN bond formation, with Co₃C-(001) most active owing to its negatively charged surface, strong N* binding, and low activation barriers of NN bond formation. Plasma-induced vibrational excitation of NH₃ and its reactive radicals promotes a radical-driven •NH₂-N* coupling pathway that dominates on Co₃C-(001) and Co₃N-(001), shifting the rate-limiting step to NH₃ ^(v₁) dissociation, increasing turnover frequencies by up to 6 orders of magnitude, and reducing the temperature needed to reach a turnover frequency of 5 s^-1 from >680 °C (Ru and Co under thermal condition) to 267 °C (Co₃C) and 415 °C (Co₃N). These results identify Co-based carbides and nitrides as promising plasma-active catalysts for energy-efficient hydrogen production from ammonia.