Choosing a liquid hydrogen carrier for sustainable transportation†

Abstract

Liquid hydrogen carriers (LHCs) are important shuttles for molecular hydrogen (H₂) as they are convenient to transport as energy-dense liquids over distances greater than 10 000 km. Herein, we provide comprehensive insights into the comparative practicality and safety of irreversible LHCs. From a gas purification standpoint, fewer products in the released H₂ stream result in less separation complexity and lower cost. Unit operational complexities of methanol (MeOH) steam reforming versus fossil steam-methane reforming were analyzed in depth to highlight gas-cleaning complexities. The main challenge is to estimate the costs of LHC reforming, cleaning and compression (RC&C) steps for H₂ production in order to break even with other energy scenarios. To achieve this, two techno-economic analyses (TEA) were performed from the ‘vehicle’ and ‘fuel’ points of view. ‘Vehicle’ analysis compares the use of MeOH-to-H₂ for proton-exchange membrane fuel-cell vehicles (FCVs) with the use of MeOH directly as drop-in fuel for conventional vehicles (ICEVs). ‘Fuel’ analysis compares renewable MeOH and dimethyl ether LHC transport with pressurized and cryogenic H₂ transport for FCVs. For the analyses in which H₂ gas is produced as a fuel, RC&C steps are assumed to be accomplished off-board or before fueling the vehicles. ‘Vehicle’ analysis findings indicate that with a moderate tax on carbon emissions, in the year 2035 and beyond, FCVs can be competitive with ICEVs with an RC&C cost of ∼US $ 2–6 per kg H₂. From the ‘fuel’ analysis perspective, LHCs break-even with gaseous and liquid H₂ transport at a more flexible RC&C cost of US $ 7.9–11.4 per kg H₂.