Ammonia has emerged as a leading candidate for transporting hydrogen across global markets due to its favorable chemical properties, existing infrastructure, and energy density. Unlike liquid hydrogen (LH2) or liquid organic hydrogen carriers (LOHCs), ammonia does not require cryogenic temperatures for storage, simplifying logistics and reducing energy costs. Its high hydrogen content by weight, approximately 17.6%, makes it an efficient medium for maritime transport. The established global trade in ammonia, with over 180 ports handling the chemical, provides a ready foundation for scaling hydrogen shipments.

Liquefaction of ammonia occurs at -33°C under atmospheric pressure or at higher temperatures with moderate pressurization, significantly less energy-intensive than LH2, which requires temperatures below -253°C. This reduces the energy penalty associated with cooling and maintaining cryogenic conditions during transit. Tanker design for ammonia leverages existing liquefied petroleum gas (LPG) carrier technology, with minor modifications to handle ammonia’s corrosiveness. Modern ammonia tankers use double-walled stainless steel or nickel-steel tanks with insulation to prevent boil-off, a challenge more acute in LH2 shipping where evaporation rates can exceed 0.2% per day.

Port infrastructure for ammonia is already well-developed, with terminals capable of loading and unloading large volumes. In contrast, LH2 requires specialized cryogenic facilities, which are limited globally. LOHCs, while storable at ambient conditions, necessitate dehydrogenation plants at destination ports, adding complexity and cost. Ammonia can be directly used in industrial applications or cracked to release hydrogen using established methods, offering flexibility in end-use.

Safety considerations for ammonia differ from LH2 and LOHCs. Ammonia is toxic, requiring strict leak detection and ventilation systems, but its pungent odor aids in early detection. LH2 poses risks of embrittlement and explosive mixtures in confined spaces, while LOHCs are generally safer but involve flammable organic compounds. Regulatory frameworks for ammonia transport are mature, governed by the International Maritime Organization’s (IMO) International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code). LH2 and LOHCs face evolving standards due to their nascent use in shipping.

Comparing energy efficiency, ammonia shipping loses less energy during transit than LH2, where boil-off management consumes additional fuel. LOHCs suffer from energy penalties during hydrogenation and dehydrogenation, reducing round-trip efficiency. However, ammonia cracking to extract hydrogen requires temperatures around 400-600°C, impacting overall energy balance.

In summary, ammonia offers a pragmatic solution for global hydrogen transport, balancing energy density, infrastructure readiness, and handling requirements. While LH2 and LOHCs present alternatives, ammonia’s integration into existing supply chains positions it as a near-term enabler of the hydrogen economy. Regulatory alignment and safety protocols will be critical to scaling its maritime use alongside emerging competitors.