A mini-review on ammonia decomposition catalysts for on-site generation of hydrogen for fuel cell applications

Due to the drive for better environmental protection and energy conversion efficiency, on-site generation of CO_x-free hydrogen from ammonia decomposition for fuel cell applications has attracted much attention. The development of high performance solid catalysts is essential for the supply of such hydrogen from ammonia. In this mini-review, we provide a summary of the reaction kinetics of catalytic ammonia decomposition. Comparisons are then made among the catalysts that have different active components, supports, and promoters. According to the works reported in the literature and our recent research results, Ru is the most active catalyst, carbon nanotubes (CNTs) are the most effective support, and KOH is the best promoter. An increase in Ru dispersion results in better catalytic performance. Both support basicity and conductivity are important criteria for a NH₃ decomposition catalyst of high efficiency; and it seems possible to generate novel advanced support, such as oxide-CNTs nanocomposite materials, that bears such characteristics. Also, proper removal of the electron-withdrawing entities that originate from the precursors of active component, support or promoter can be effective in enhancing the catalytic activity of a Ru catalyst.