Hydrogen is often seen as the fuel of the future on account of its zero-emission and high gravimetric energy density, meaning it stores more energy per unit of mass compared to gasoline. Its low volumetric density, however, means it takes up a large amount of space, posing challenges for efficient storage and transport.
In order to address these deficiencies, hydrogen must be compressed in tanks to 700-bar pressure, which is extremely high. This situation not only incurs high costs but also raises safety concerns.
For hydrogen-powered fuel-cell vehicles (FCVs) to become widespread, the US Department of Energy (DOE) has set specific targets for hydrogen storage systems: 6.5% of the storage material’s weight should be hydrogen (gravimetric storage capacity of 6.5 wt%), and one liter of storage material should hold 50 grams of hydrogen (a volumetric storage capacity of 50 g L‒1). These targets ensure that vehicles can travel reasonable distances without excessive fuel.