Guiyan Zang, Massachusetts Institute of Technology (MIT)
Hydrogen is expected to be the next generation fuel and the development of safe and highly efficient global hydrogen supply chains is of critical importance. The use of hydrogen carriers is a promising strategy to ensure safe storage and transport of hydrogen. Liquid-phase hydrogen carriers such as methane and methanol are considered suitable candidates and several studies detailing their effectiveness as hydrogen carriers have been recently reported. They are produced by reacting hydrogen with CO2 obtained from Direct Air Capture (DAC) or industrial waste, and offer a reasonable alternative to liquid hydrogen for hydrogen storage and transportation. However, they also pose challenges with regard to re-hydrogenation, safe long-distance transport and overall reduction of global GHG emissions. A possible alternative is utilizing solid materials that are capable of storing and carrying hydrogen energy. These solid-phase hydrogen carriers are generally metals that are ‘hydrogenated’ at the departure point, transported in bulk carriers and ‘dehydrogenated’ at the arrival point. The energy requirements and the equipment needed for the hydrogenation and dehydrogenation processes differ significantly from one carrier to another and a detailed supply chain analysis under a common framework is lacking in literature.
In this study, we discuss two solid-phase hydrogen carriers: magnesium hydride and aluminum. The hydrogenation and dehydrogenation processes for the carriers are designed and optimized as part of the hydrogen supply chain. The hydrogen supply chain is built from Australia to Japan and techno-economic analysis and life cycle analysis are performed along a common framework to estimate the costs and emissions of hydrogenation, storage, oceanic transportation and dehydrogenation of the carriers. The levelized cost and GHG emissions of the solid-phase carriers are compared against liquid-phase carriers methane and liquid hydrogen, in order to determine the economic and environmental feasibility of utilizing solid-phase carriers. The analysis shows that hydrogenation and dehydrogenation processes contribute significantly to the overall costs and emissions of the hydrogen supply chain when solid-phase carriers are used. Technological advancements to improve process efficiencies are needed to ensure full utilization of the advantages provided by solid-phase carriers. The results from this study provide a comparative assessment of solid-phase and liquid-phase hydrogen carriers that we hope can provide industry and academic researchers with the required knowledge and guidelines to develop efficient global hydrogen supply chains.
