Green ammonia as a hydrogen carrier: integrating production pathways, storage technologies, and techno-economic trade-offs

The transition from fossil fuel to renewable hydrogen production is shifting ammonia from its conventional role as an industrial chemical toward a large-scale energy and hydrogen carrier. This transition changes the requirements imposed on ammonia storage, as emerging supply chains involve larger inventories, variable renewable production, prolonged storage, frequent transfer, marine transport, distributed demand, and closer interaction with energy infrastructure. Storage technology must therefore be considered as an integral component of the hydrogen–ammonia value chain rather than as an isolated containment problem. This review develops a physics-based framework linking ammonia thermodynamics to containment design, thermal management, material integrity, release behaviour, safety, and lifecycle economics. Pressurized, semi-refrigerated, and fully refrigerated storage are examined as different responses to the same pressure–temperature equilibrium rather than independent technologies. The analysis shows that decreasing storage temperature does not eliminate engineering complexity but redistributes it: structural and pressure-management requirements progressively give way to refrigeration, insulation, boil-off management, low-temperature integrity, and utility dependence. Conversely, warmer storage reduces thermal-management requirements while increasing containment pressure, equilibrium flash fraction, and pressure-related consequences of loss of containment. These interactions prevent storage capacity alone from defining an optimal technology. A multidimensional selection framework is therefore developed in which inventory, holding duration, transfer duty, mobility, utility availability, land constraints, safety consequences, infrastructure integration, and lifecycle cost jointly determine the preferred storage regime. For applications requiring molecular hydrogen at the point of use, the review further examines ammonia cracking, reactor and catalyst requirements, membrane-assisted conversion, and hydrogen purification, highlighting the additional energy and system-level penalties associated with downstream reconversion. By connecting thermodynamic fundamentals with system-level engineering decisions, the review establishes ammonia storage as a coupled optimization problem within emerging green hydrogen and ammonia supply chains and identifies the research priorities required for their safe and economically scalable deployment.