Unraveling the Dual Dependence of Surface and NH ₃ Concentration on Cobalt-Catalyzed Ammonia Decomposition

Ammonia decomposition offers a promising route to carbon-free hydrogen, yet its activity is highly sensitive to both surface structure and NH3 concentration. This dual dependence makes it challenging to design catalysts that remain high efficiency throughout the entire process. Here, we systematically evaluate all potential exposed surfaces and establish an atomistic framework for linking structure–activity relationships across varying reaction stages on cobalt, a widely used ammonia decomposition catalyst. A clear surface-dependent reactivity is identified, with stepped HCP Co(10–10) and FCC Co(110) being the most active, and Co(10–10) consistently outperforming others, indicating that enriching this surface can enhance overall performance. Mechanistically, surface sensitivity is primarily attributed to variations in the d-band center, which correlates linearly with activity. Furthermore, we propose a general criterion of Arrhenius slope (−1/RT), revealing that NH3 concentration dependence stems from shifts in the rate-limiting step, transitioning from N–N coupling to alternative steps as NH3 concentration increases.