No Time for Nitrides: How Cobalt Alloying Promotes Iron Catalysts for Ammonia Decomposition

The increasing demand for sustainable hydrogen production has driven interest in ammonia decomposition. Iron-based catalysts, widely used for ammonia synthesis, exhibit suboptimal performance in the reverse process due to their tendency to form iron nitrides. Alloying iron with cobalt has been reported to enhance catalytic activity, but the underlying microscopic mechanisms remain unclear. In this study, we employ machine learning-based molecular dynamics simulations and experimental validation to investigate the role of Fe-Co alloying in ammonia decomposition. Our simulations reveal that cobalt alloying into iron catalysts provides a dual promotional effect: it slightly lowers the free energy barrier for nitrogen recombination, which is the rate-determining step in ammonia decomposition, while significantly suppressing nitrogen migration into the bulk, thereby preventing nitride formation. These findings are corroborated by transient decomposition experiments and desorption measurements, which demonstrate enhanced activity and resistance to nitridation in FeCo alloys compared to monometallic iron catalysts. Our results provide fundamental atomistic insights into the synergistic effect of Fe-Co alloying, offering a pathway for the rational design of more efficient catalysts.