From a mechanical perspective, designing a hydrogen storage system is significantly more complex than a diesel storage system. Hydrogen has more storage options available however, it presents higher risks than diesel such as greater flammability and explosivity, higher pressures, potential for low temperature, or chemical storage methods which are all hazardous. This therefore requires the mechanical design for such a system to comply with rigorous safety standards.
Ok, so h2 unsurprisingly is wast more explodey, and hard to store safely and cheaply