A volumetric density of 70.8 kg/m3 can be achieved using 15.2 kWh/kg of energy as work through a process of compression and cooling in cryogenic tanks while the gravimetric density is influenced by the tank size. In Type 3 (metal-lined) cryogenic tanks, a 2-mm stainless steel liner meets the 15,000-fatigue cycle life requirement for storage pressures up to 700 bar. Because these physical methods of H2 storage do not typically meet applicable safety and/or density requirements, especially for transport applications, chemical hydrogen storage methods have received the widespread attention of scientists. Hydrogen storage materials can be divided into two categories based on the relative strength of the material interaction with hydrogen: "physisorption materials" and "chemisorption materials." In physisorption materials, H2 molecules are adsorbed via a weak van der Waals interaction on the surface of the pores. The physisorption process is reversible since the interaction energy is incredibly low. A dominant material in this class are carbon sorbents where physisorption is proportional to their specific surface area. Storage pressures for physisorption based sorbent systems can be much lower than physical storage methods without a significant reduction in capacity. Storage temperatures can also be higher, thus reducing the cost for insulation and the energy consumption for cooling. Lastly, sorption is a completely reversible process and does not require off-board regeneration as is needed for chemical storage options. The main challenge for physisorption materials is low binding energy for H2. An approach is to use cryogenic temperatures to enhance gravimetric and volumetric storage capacities of physisorbents, although this comes at the cost of some of the benefits. In chemisorption-based materials, hydrogen chemically interacts with the storage medium. Chemisorption process may not be fully reversible due to relatively high activation energy in the adsorption and desorption process. On-board hydride materials belong to this class. In contrast to green hydrogen production, the number of annual publications on H2 storage is steady at about 1500 with yearly fluctuations between 2011-2021 (Figure ). However, this total hides the declining number of journal publications. The surge of the 2012-2013 publications coincides in time with the first commercially produced hydrogen fuel cell vehicle, Hyundai ix35 FCEV, introduced by Hyundai in 2013. A decrease in journal publications occurred up to 2017. Since, journal increases occur through 2021. At the same time, the number of patents shows more steady growth with fewer fluctuations. The growth of patents may indicate a special interest of manufacturers such as Toyota, Honda, Hyundai, and Panasonic in developing new on-board H2 storage technologies (see Table ).