Ni-based alloy catalysts for cost-effective hydrogen production from ammonia decomposition

• The catalytic activity of 3d monometallic and Ni-M ( M =Co, Fe) catalysts for NH 3 decomposition is investigated. • The correlation between N adsorption energy and the catalytic activity of the catalysts is elucidated. • d-band filling can be used as a simple descriptor to predict the catalytic activity for NH 3 decomposition. • A Ni 0.64 Fe 0.36 alloy is suggested as a cost-efficient catalyst for H 2 production via NH 3 decomposition. Due to its high hydrogen storage capacity and established infrastructure, ammonia (NH 3 ) decomposition has been extensively investigated as a clean hydrogen production process. However, hydrogen production via ammonia decomposition faces various challenges. Although ruthenium (Ru) catalysts exhibit the highest activity for ammonia decomposition, their scarcity and high cost hinder commercial application. Consequently, nickel (Ni) catalysts have emerged as a potential alternative, owing to their cost-effectiveness and high activity. To further optimize Ni catalysts, developing Ni-based alloy catalysts with other metals is a promising solution. Herein, density functional theory (DFT) calculations are performed to elucidate the catalytic activity of 3d transition metals (Ni, Co, Cu, and Fe) and their promising alloys. The key reaction steps of overall ammonia decomposition are NH x ‒H bond scission (NH x *→NH x-1 *+H*) and N + N recombination (N*+N*→N 2 *). In particular, nitrogen adsorption energy (E ad (N)) serves as a descriptor for predicting the activation energies of key elementary steps, revealing a volcano-like relationship between experimental catalytic activity and DFT-calculated E ad (N). Additionally, we discover a strong correlation between d-band filling (f d ) and E ad (N), establishing f d as an effective descriptor that not only predicts E ad (N) but also the catalytic activity of NH 3 decomposition. Our descriptor-based design principle identifies Ni 0.64 Fe 0.36 as a potentially effective and cost-efficient candidate for hydrogen production from ammonia, with experimental data demonstrating its superior performance compared to pure Ni. These findings offer valuable insights into the development of efficient, economically viable transition metal-based catalysts for hydrogen production through ammonia decomposition.