Synergistic catalysis of CoN sites and Co nanoparticles for efficient COx-free hydrogen production from ammonia decomposition

A series of carbon-based Co catalysts was designed for hydrogen production from ammonia decomposition. Notably, the CoCe-NC catalyst exhibited the superior activity, achieving complete NH₃ decomposition at 600 °C with a remarkable hydrogen production rate of 1,840 mmol·g_cat⁻¹·h⁻¹. Advanced characterization techniques, including XRD, Raman, XPS, EXAFS, and CO-TPD, were employed to analyze the surface Co species of these catalysts. The active species present on the Co carbonaceous catalyst surface include CoN, Co nanoparticles (NPs), and larger metallic bulk. The confinement of metal–organic framework (MOF) precursor plays a crucial role in the formation of Co NPs. Moreover, it was found that N and Ce doping in the carbonaceous substrate effectively promoted the formation of Co NPs and CoN structures. DFT simulations of the ammonia decomposition behaviors upon various active species were conducted, verifying that Co NPs serve as the optimal active sites. Furthermore, it was discovered that CoN, with relatively poor self-catalytic ability, synergistically catalyzed the ammonia decomposition with Co NPs, effectively decreasing the energy barriers for recombination of both N₂ and H₂.