The Potential Role of Ammonia for Hydrogen Storage and Transport: A Critical Review of Challenges and Opportunities

Hydrogen is being included in several decarbonization strategies as a potential contributor in some hard-to-abate applications. Among other challenges, hydrogen storage represents a critical aspect to be addressed, either for stationary storage or for transporting hydrogen over long distances. Ammonia is being proposed as a potential solution for hydrogen storage, as it allows storing hydrogen as a liquid chemical component at mild conditions. Nevertheless, the use of ammonia instead of pure hydrogen faces some challenges, including the health and environmental issues of handling ammonia and the competition with other markets, such as the fertilizer market. In addition, the technical and economic efficiency of single steps, such as ammonia production by means of the Haber–Bosch process, ammonia distribution and storage, and possibly the ammonia cracking process to hydrogen, affects the overall supply chain. The main purpose of this review paper is to shed light on the main aspects related to the use of ammonia as a hydrogen energy carrier, discussing technical, economic and environmental perspectives, with the aim of supporting the international debate on the potential role of ammonia in supporting the development of hydrogen pathways. The analysis also compares ammonia with alternative solutions for the long-distance transport of hydrogen, including liquefied hydrogen and other liquid organic carriers such as methanol.