Ammonia as a Hydrogen Carrier: Advances in Storage, Catalytic Decomposition, Kinetics, and Techno-Economic Analysis

Abstract

A carbon-free energy system might use ammonia as a hydrogen carrier owing to its high hydrogen concentration, good liquefaction, and worldwide production and transportation infrastructure. Catalytic ammonia breakdown provides a CO₂-free hydrogen-generating method, but high temperatures, catalyst deactivation, and expense restrict its practicality. This study covers important aspects of ammonia decomposition catalysts, including Ru-, Ni-, and Co-based systems supported by carbon, Al₂O₃, and perovskite oxides. To develop structure–activity connections and identify rate-limiting stages under various operating regimes, thermodynamic, kinetic, and fundamental reaction processes are examined. Ru-based catalysts, especially those supported on conductive carbons and tailored perovskites, are standards for low-temperature activity, but their high cost and stability prevent large-scale application. Combining Ni-based catalysts with Al₂O₃ or basic perovskite supports offers a good balance between activity, cost, and commercial practicality, making them the dominant non-noble alternatives. Due to strong metal–support interactions and alternate reaction routes, Co-based catalysts in perovskite formulations seem promising despite being inherently less active. Support chemistry, promoters, metal dispersion, and oxygen vacancies are discussed, along with low-temperature operation and scale-up problems and research prospects.