The critical role of Fe 3d–N 2p orbital hybridization in ammonia decomposition on graphene-supported Fe₆N_<i>x</i> clusters: a DFT study

Ammonia (NH₃) is a promising carbon-free hydrogen carrier, but lowering the temperature required for its catalytic decomposition to produce H₂ remains a challenge. The main obstacle is the strong adsorption of nitrogen (N) on the active sites, which can remain on the catalysts' surface and lead to poisoning. Using first-principles calculations, we investigate the effects of N accumulation on Fe₆ clusters during NH₃ decomposition and aim to develop strategies to mitigate N poisoning. Graphene-supported Fe₆ clusters mitigate N poisoning by reducing Fe-N interaction strength, thereby improving NH₃ decomposition efficiency. The energy barriers of the graphene-supported Fe₆N_<i>x</i> (<i>x</i> = 1, 2) clusters' rate-limiting step have been reduced below 2 eV, compared to those calculated for the pure Fe₆ cluster (2.08 eV) and the graphene-supported Fe₆ cluster (2.53 eV). The rate-limiting step involves the Fe 3d-N 2p hybridization, during which an adsorbed N atom migrates across the Fe-Fe bond and combines with another N atom to form N₂. This study provides new insights into the potential application of graphene-supported metal catalysts for NH₃ decomposition.