Hydrogen production via photocatalytic ammonia decomposition

Ammonia, as a carbon-free fuel and promising hydrogen carrier, has attracted significant attention in the context of a net-zero-emission scenario. Photocatalytic ammonia decomposition is a promising approach for hydrogen production, and much attention has been given to this area in recent years. This mini-review summarizes the latest research progress in photocatalytic ammonia decomposition for hydrogen production. We mainly focus on the photocatalytic decomposition of aqueous ammonia solution and gaseous ammonia. For aqueous ammonia solution, various semiconductor-based catalysts are introduced, and the role of water is discussed. The formation of the ˙NH₂ radical as a key species in the decomposition was proposed by different groups. In the case of gaseous ammonia, different types of catalysts, including semiconductor-based and localized surface plasmon resonance (LSPR)-based ones, are described. The mechanisms of ammonia decomposition, such as N-N recombination and N₂H dehydrogenation, are discussed. Methods for accurate temperature measurement in the photocatalytic process are summarized. We conclude that photocatalytic ammonia decomposition has unique advantages, including high activity, mild conditions, a green process, and fast response. Moreover, an excellent catalyst, efficient utilization of light, and suitable reactor design are critically important for the practical application of photocatalytic ammonia decomposition.