Evaluation and Outlook for Australian Renewable Energy Export via Circular Liquid Hydrogen Carriers

To combat global temperature rise, we need affordable, clean, and renewable energy that does not add carbon to the atmosphere. Hydrogen is a promising option because it can be used as a carbon-free energy source. However, storing and transporting pure hydrogen in liquid or gaseous forms is challenging. To overcome the limitations associated with conventional compressed and liquefied hydrogen or physio-chemical adsorbents for bulk storage and transport, hydrogen can be attached to other molecules known as hydrogen carriers. Circular carriers, which involve the production of CO2 or nitrogen during the hydrogen recovery process, include substances such as methanol, ammonia, or synthetic natural gas. These carriers possess higher gravimetric and volumetric hydrogen densities (i.e., 12.5 wt% and 11.88 MJ/L for methanol) than cyclic carriers (i.e., 6.1 wt% and 5.66 MJ/L for methylcyclohexane (MCH)) which produce cyclic organic chemicals during dehydrogenation. This makes circular carriers particularly appealing for the Australian energy export market. Furthermore, the production-decomposition cycle of circular carriers can be made carbon-neutral if they are derived from renewable H2 sources and combined with atmospheric or biomass-based CO2 or nitrogen. The key parameters are investigated in this study focusing on circular hydrogen carriers relevant to Australia. The parameters are ranked from 0 (worst) to 10 (best) depending on the bandwidth of the parameter in this review. Methanol shows great potential as a cost-effective solution for long-distance transport of renewable energy being a liquid at standard conditions with a boiling point of 64.7 °C. Methane is also an important hydrogen carrier due to the availability of natural gas infrastructure, and its role as a significant export product for Australia.