Optimal Hydrogen Carrier: Holistic Evaluation of Hydrogen Storage and Transportation Concepts for Power Generation, Aviation, and Transportation

The storage of excess electrical generation, enabled through the electrolytic production of hydrogen from water, would allow “load-shifting” of power generation. This paves the way for hydrogen as an energy carrier to be further used as a zero‑carbon fuel for land, air, and sea transportation. However, challenges in hydrogen storage and transportation ultimately pose restrictions on its wider adaption along horizontal and vertical vectors. This paper investigates chemical energy carriers ranging from small molecules such as ammonia and methane to formic acid as well as other more complex hydrocarbons in response to this timely engineering problem. The hydrogenation and dehydrogenation of such carrier molecules require energy lowering the effective net heating value of hydrogen up to 32 %. Different carrier approaches are discussed in the light of availability, energetics, water requirements, and suitability for applications in power generation, shipping, trucking, and aviation, supplemented by a comprehensive safety review making this study unique in its field. It is found that hydrogen delivered without a carrier is ideal for power generation applications due to the large quantities required. Aviation would benefit from either ammonia or hydrogen and is generally a field challenging to decarbonize. Ammonia appears also to be a good medium for shipping hydrogen between continents and to power container ships due to its high energy density and lower liquid temperature compared with hydrogen. At the same time, ammonia can also be used to power the ship's engine. Long-haul trucking would benefit the most from cryogenic or compressed hydrogen due to the lower quantities required and purity requirements of the fuel cells.