A review on the recent developments of ruthenium and nickel catalysts for COx-free H2 generation by ammonia decomposition

The emerging H2 economy faces storage and transport challenges, and the use of ammonia (NH3) as a COx-free source of H2 via NH3 decomposition has recently attracted attention. Noble Ru-based catalysts are considered the best choice for highly efficient NH3 decomposition; however, their high cost and limited availability are disadvantages in large-scale applications. Otherwise, among non-noble metal-based catalysts, Ni-based catalysts are the most active, and Ni is considered a good alternative candidate material for NH3 decomposition because of its low cost. At present, some challenges remain in efforts to improve the efficiency of both Ru- and Ni-based systems. This review covers recent developments regarding these catalysts and can serve as a comprehensive work for evaluating effective long-term strategies.