Paul Martin, chemical engineer and process development expert, explains the challenges of using hydrogen as a fuel.

When you start looking in earnest at hydrogen as a fuel, it becomes apparent that it is a fuel which is difficult to move and store, and its energy density per unit volume under all conditions is extremely poor, even though the energy density of hydrogen per unit mass is excellent.

The most obvious options are high pressure gas storage and making liquid hydrogen (LH2). For transportation fuel uses, compressed gas storage is the least bad of a terrible set of choices. However, even at 700 bar (10,000 psig or 5 tons per square inch of pressure), hydrogen is still only 41 kg/m3.